batteryacid Yeah one of the big things to look for is a guide that maintains a right angle well. The best way, IMO, to figure this out is to just look for a creaser where the guide looks like it is properly anchored. But maybe others will have better ideas, or examples / pictures.
On our creaser (which we inherited a long time ago, without having done any real research or thought), the guide only has one thumbscrew holding it in place, so it freely pivots along this point and is really bad at maintaining a right angle. To mitigate the problem we use magnets to hold it in place, but it's still a pain and we have lots of weird tricks and muscle memory to make it work correctly.
Another thing to consider is that some creasers can put 2 or even 4 creases into a sheet of paper in one motion, reducing the work you have to do by half or 3/4. Pretty nice!