I have the Clymer book, it covers lots of Honda's. Never used the other repair manuals or tried them so I can't say much about them. I've got quite a bit of experience working on stuff so I know the basics of how the things work with each other and how motors work, etc, but I love the pictures in the Clymer book because it shows all the little details and gives a visual. I'm just a visual learner so it helps me a lot. In specific, it helps me from forgetting little tiny spacers and stuff like that in the motor, or something like that where you really need to be 100% sure on what you're doing. I've rebuilt tons of these bikes now, and I still refer to the Clymer book from time to time just to be sure. I've done so many top end rebuilds I could do them in my sleep, but every now and then I will skip a step and overlook something stupidly obvious just because I go into auto-pilot. Never a bad idea to have it near by just in case. My Clymer book has always provided me the info I've needed, but I do refer to parts break downs from time to time depending on what exactly it is you are trying to find or figure out. One thing to look out for is that the Clymer book splits it into sections...so for example, you are looking up something on the clutch....Just be sure you are on the correct page and looking at the right diagram for the model you are working on. Not a big deal usually because the pictures will look different from what is in front of you, but when looking up something like the clearances when adjusting the valves, you could be looking at the wrong info for the bike you are working on if you aren't careful. Overall a very well organized book. 10/10.
They both look pretty good, But I'd steer you towards Clymer....They have a well known name and it provides you with multiple models. I don't know of many people with a Z50 that don't have a few more bikes!

I'm sure the other one is good too though. Looks to be pretty well organized as well. If whichever book you go with doesn't help you out enough, you can get lots of advice and tips from other mini enthusiasts here on PM.
Best of luck with your minis!
Aaron