Not sure what you mean by 1 or 3 stars but cyclinder guards are there to stop drilling and hammer attacks*. This doesn't effect the type of cylinder you use, but as with all things, you generally get what you pay for with locks.
Is your cyclinder offset, i.e. longer on one side? They're the critical measurements you need.
*Sounds impressive and it can be, if you're using a steel door. It took the SAS two and a half minutes to break throught one of our steel security doors once, and trust me, that was a long time for them. The element of suprise would have been completely gone and in the end they just put some det cord on and blew it up! Not very subtle but effective and as a young lad back then (this was mid 80s) having the SAS visit the factory was seriously cool.
On a UPVC door cyclinder guards ain't going to help. The basic structure of the door just doesn't stand a serious attack. At the end of the day the plastic will buckle and bend way before the metal gives up the ghost.
