the crrc pro engine is not a bad engine,just make sure that everything is tight,ie all bolts etc etc.you get what you pay for really,
the better option is of course the zen,good cheap ones come up now and then second hand on ebay,or there is the zen copy from china which i happen to know someone who has bought one of them and it seems to go very well indeed,
they stink zenoah just without the name,if you know what i mean,also dont rule out the sikk 27 engines,i have used these for many years and found them to be very good indeed and with abit of tuning to be very fast as well,it all boils down to what you are using it for?
you should get your money back on the crrc pro without a problem should you decide to go down the zen route,hope this helps ?
kurt black magic racing