I was not much of a believer in the round pin is better than the pressed steel butterfly type debate, but after some drama trying to get a Squier deluxe to settle back in tune after swinging on the bar I gave these a go.
To mark the position of the pin hole I just fitted the guides where they needed to be and added a few turns to the screw. This marked the head stock with a small dent to show where to drill. Simple..... Or not so in my case.
Guide number one went in true, aligned perfectly and screwed down flush. On to guide #2. With a 1.5mm Ø bit in the worlds biggest drill at around 3mm deep, the guitar slipped and the drill bit snapped, flush with the surface. Not a problem, it felt pretty loose, Ill ease it out with a round needle file. Five minutes later with the drill bit firmly wedged in place with a broken hardened file point stuck beside it I went to plan B. The beauty of these things is the casting on the main body is pretty soft, two minutes with a flat file and the pin was gone. The guide minus the pin does not rotate at all and the strings keep it in place anyway.
These guides work. Are they better than pressed steel? I dont know, it depends on the guitar. I have a HB ST-62 which is fine with the butterflies so I wouldnt change them. The Squier had a problem returning to tune, these have improved that. Would I buy again? Yes, if the guitar needed them.
Pros:
Look pretty good.
Does improve tuning stability on certain guitars.
Pin is easy to remove if you dont want to drill the head stock.
Cheap enough for what they are.
Cons:
id say normally if all goes well none. If you mess up like I did, the con is its the fact you need to drill to fit. Maybe they could rectify this by making the pin a short spike? The screw would then drive that into the wood. In hindsight, finding out how soft the metal is, I would have filed the pin into a point and done it that way.
Overall a good guide that in normal circumstances is easy enough to fit and frees off the strings. They do what they say they do and do it pretty well.