At this point, the only engine in the OS AX series is the .46AX. It replaced the OS .46FX.

The AX is a top-of-the-line, mid-sized engine. It has good power. It is very high quality, very reliable, easy to start and easy to adjust. It is more expensive than the Chinese engines of the same size and you'll need to make the judgement at to whether it is worth the extra money.