Turntable Speed

The operative word is "pretty", as in "pretty accurate".  Most of us are looking for speed errors or more importantly speed variation of less than 0.1 RPM against a background of 33.XX RPM.  I am mostly basing my claim on reports of others who first monitored speed with a cell phone and then used other more accurate methods, e.g. the Sutherland Timeline or the Phoenix Engineering Roadrunner or even the KAB, and found that the cell phone app in question was off a bit.  I don't think absolute exact 33.333 rpm is a necessary goal. I do think that keeping speed constant within a very small bandwidth is much more important, as we are much more sensitive to warble than to absolute pitch.  For starters, the cell phone itself does not match the actual load of an LP being dragged by the stylus, neither in weight nor in distribution of mass.

Turntable speed for me needs to be accurate enough to tune and play a guitar to.  If the band is playing in "E", I want to be able to tune my guitar (using a tuning fork) and solo along to that (given a modern recording where the band had the right pitch in the first place.)   My KAB strobe gets me there, although I acknowledge it's not 100% accurate.

Only product I know that's VERY accurate is the Timeline device. Don't know if it's still made.
https://youtu.be/RF2XieUlzvk

Timeline itself is accurate. The problem with it is that it relies on a human being to assess its accuracy by following a laser dot on a wall. Probably the timeline is better than the observers of the timeline.

I have a mint condition Yamaha P-550 turntable that I bought new in 1983 that also has the strobe light adjustment.  I had it completely serviced to set up a turntable system for my youngest son a couple of years ago, and it dials in the speed like butter now.  Very nice, low maintenance, budget turntable.