does this mean dont turn engine over until tensioner is engaged
It means they don't know how to write a good instruction. Anyone who has picked up one of my Krieger Cam Chain Tensioner units would tell you that. One rider commented that the instructions I send could be followed by anyone who knows which end of a screw driver to hold.
As for manual versus "automatic" the question is more if you want to have to mess with something that shouldn't need to be messed with - it's automatic, after all - and hope it continues to work as you ride the bike or if you want a solid unit with a fixed adjustment that you know is working.
My instructions tell you to turn the adjuster bolt in finger tight. Since few people in the world can generate more than an inch/pound or two of tightness by finger tightening an 8mm bolt, it is highly unlikely that they will overtighten the adjuster. The problem I see is when you get someone who seems to think it should be tighter, because finger tight doesn't seem tight enough - why do they think there is a locking nut on the part?
It's all about doing a good job of writing work instructions, which I happened to do for a cutting tool company. It's also about having the engineering knowledge to understand what is going on and how the parts need to work together when writing them along with a willingness to work with riders. This I have done over the years, ranging from answering questions on-line and by phone. The last four tensioners I've developed came by rider requests. The Kawasaki KLX250, Honda Superhawk/Firestorm/CBR, Yamaha XS1100, and Yamah XS850. I started in this whole thing because that one company didn't bother getting with me when I asked if they could simply put a longer bolt into their GPz550 tensioner body. They didn't help, so I did it myself and made a few extra. Demand grew. As people learn more about the cam drive system and how all of it works, the manual tensioner becomes the obvious choice when the OEM fails.
Of course I will say, "if it ain't broke don't fix it." But when the part does fail, do what the racers do, get a simple part that will work reliably. They don't want to break in the race andyou don't want to break hundreds of miles from home. Same difference - both ruin your day.