I've used this style cleat for approximately 25 years and like it. With the purchae of new shoes I thought also time to buy new cleats.
The release is a bit tighter than I am used to with my old well worn cleats...guess that's to be expected. Hope for a short break in period to ease the effort necessary for release.
Previously I had used the SH-56 multi-release cleats, but had encountered instances of coming unclipped when I didn't intend to. Was buying new shoes and decided to try the SH-51 cleats this time. The connection feels much more secure than the multi-release version, but still easy enough to clip in/out.
If you're new to clipless or commuting with a lot of stop-and-go then SH-56 might be better, but otherwise I would recommend the SH-51.
I have these cleats attached to my Shimano winter biking boots. Very effectively, no unexpectedly sliding around with the pedals & no problems having them get stuck in place when I stop at lights. So no fear of falling over (because of cleats & bike shoes in any case.