Actually I consider the Zenit-B or E a nice camera for basic training. The body seems undestructable and one can see how the mechanics work. Though due to the applied concept of shutter mechanics these models only have the fast range of shutter times. The lack of an automatic diaphragm but the existence of a pre-set stop for minimum diaphragm might even be beneficial for training.
The release-button lock is something to warn about: once locked and incidentially twisting the cocking lever thereafter, after unlocking and cocking the shutter will not cock totally and the mirror will not go up at all. At the second release the mirror will go up but the shutter still will not be cocked fully, only the third exposure will be right again.
With this in mind and the fact that the shutter must be released bevor it can be locked, one better not uses that lock at all.
There may be slight variations depending on year of built. Furthermore both camera and Helios lens were manufactured at various plants, further introducing further, minor variations.
(One of my Zenits got a cocking lever rewind spring that lost part of its tension. It seems I'm not the only one to encounter this. The cocking lever already got a long stroke (230°). With the release-button locked you can even twist it (without load) 270°. Maybe that spoils that spring.)