"Not for the faint hearted!" My honest review of the new Mizuno Pro S-1 iron

I put the Mizuno Pro S-1 irons through their paces to find out if the Pro 241 upgrade will maintain the legendary iron manufacturer’s iconic status in the players’ irons category.

With the Mizuno Pro S-3 Irons starting the new family at the beginning of 2025, Mizuno have hit the ground running in a pivotal year for major golf equipment manufacturers. The Mizuno Pro S-3 had a distinct identity, and the Mizuno Pro S-1 irons have followed suit.

As with any Mizuno iron, there are high expectations from tour players and consumers alike. The best Mizuno irons feature clean, soft models, promoting high performance in a head that oozes premium.

The Mizuno Pro S-1 ticks all the boxes for the legacy of the brand, but it’s still not a club I’d recommend for a lot of amateur golfers. That being said, it’s certainly an iron set I aspire to game.

Looks/Feel – 4.5/5

The Mizuno Pro 241, this iron’s predecessor, received high praise as a glossy players’ iron that represented Mizuno’s identity perfectly, down to each groove on the face. The Mizuno Pro S-1 features some aesthetic changes that push it towards the tour validation concept for this signature iron.

My first thought when looking at this iron down at address was the shaping, from its size to distinct geometry. The toe felt sharper, which I later learned was a request from tour players Ben Griffin and Keith Mitchell. Having played irons with a square toe for some time, this suited my eye straight away.

What really stood out to me was the blade length of the Mizuno Pro S-1 iron. Although it isn’t a significant shift away from the design of the Mizuno Pro 241, the shaping made the blade length seem a lot smaller. Having tested the Titleist T100 irons in recent weeks, I noticed this model is significantly smaller overall, which made me question how the club would feel across the face.

Mizuno irons normally have a distinct feel off the face due to their innovative technology, and while the Pro S-1 model has that, it was on the firmer side of the Mizuno iron spectrum.

Don’t take this as a negative – the firmer feel coupled with the Mizuno DNA has a tour personality to it, reminding me of some older Mizuno irons from the 2010s era.

Unsurprisingly, these feel very different when you do mishit them. They aren’t designed to be forgiving, although that has improved. My toe strikes were particularly cruel from a feedback point of view, but that’s understandable a one-piece forged blade.

Technology – 5/5

The players’ iron category always features an array of exciting technological marvels, packing various types of performance enhancements in a small, compact head. The Mizuno Pro S-1 irons have built on the technology of the Pro 241 from tour and amateur feedback, leading to a model that is supposedly more forgiving whilst promoting elements that tour players would prefer.

The Mizuno Pro S-1 features a new Channel Back design, aiming to enhance the vertical stability of the iron, essentially leading to higher vertical MOI. This mass redistribution, coupled with Mizuno’s Harmonic Impact Technology, essentially creates a club that provides a lot of feedback and higher vertical forgiveness.

This is still targeted at the accomplished golfer, with horizontal MOI not being changed for this iteration. It’s a smart, well-engineered concept that I noticed when testing at Dundonald Links. Don’t be fooled, though; the increase in vertical stability doesn’t make this significantly different from other pure musclebacks.

Another interesting technological improvement we see from the Mizuno Pro S-1 iron focuses on the sole. It has been made flatter with a sharper leading edge, whilst increasing the bounce by 1 degree. What this achieves is improved turf interaction for the shallower players, whilst also reducing the chance of digging for other golfers, creating an iron with all-around performance for turf interaction.

I don’t have the shallowest of attack angles, but with my testing on the burnt links turf of Dundonald I did not see any digging or bouncing back from the irons, which I’ve experienced before in other blades. So far, this iron ticks all the boxes for the low handicapper.

Performance 4.5/5

What Mizuno do so well with their Pro range is providing clear intent with each model whilst allowing the option for them to be blended together to heighten performance.

Whilst this is still the case in their signature series, I do find myself separating the Pro S-1s away from the Pro S-3s. The Mizuno Pro S-1s are an absolutely gorgeous set of irons, but even as a 4-handicap, they do provide some intimidation. The long irons need to be seen in person to truly understand, and I’d scarcely recommend those to an amateur golfer unless I see the wear marks on your current irons first.

This element is further reflected in the performance. I had several testing sessions with the irons at Dundonald, hitting on a Foresight GC Quad to establish initial data. Whilst these irons still generated impressive ball speed, matching the Titleist T100s at 138mph for a 7-iron, the variance jumped out at me.

I had a drop off of up to 15 mph on mishits, and although the spin was impressively consistent for these poor shots, the overall distance suffered as a result. You shouldn’t expect groundbreaking forgiveness in a muscleback iron, but I certainly felt this was on the lower side in that category.

That doesn’t mean the shorter irons aren’t attainable for a low handicap amateur golfer, and I’d certainly be delighted gaming them in my scoring clubs.

Overall – 4.5/5

Mizuno had a clear aim with the Pro S-1 irons, and they have succeeded in adding a tour-validated weapon into their signature series for 2025. I imagine this model to be what all low handicap golfers strive to have in their bag – a pure muscleback from top to bottom, offering all-around performance for a high-performing ball striker. For the most part, I’d usually push an amateur golfer to the Mizuno Pro S-3s for that added element of forgiveness. A combo set of the S-3s and S-1s will be appealing to a lot more golfers, myself included.

Mizuno Pro S-1 Irons

RRP: $215/£215 per iron

Availability: 4-PW – all in right-handed an left-handed.

7-iron loft/lie/length: 34º / 62º / 37.25"

Stock shaft: KBS Tour 120 (S)

Stock grips: Golf Pride Tour Velvet