I had a couple of the "1st" generation 440 clones from vegas karts. Both self destructed almost imediately. Neither was built much at all. No RPMs over 6500 ever turned. Both had super thin blocks. They would just break with very little effort. The true Honda blocks are vastly superior to the clone 420 blocks. Much stronger and better tolerances. The "2nd" generation 440s are in at vegas Karts. They have a completely different block design and are suppose to be much better. Havent tried them. The "new" block made them illegal for my use. Definately easy to identify as not being a 390/420.. I would think an MX 450 would be way more reliable and all around "better" than a big block GX style. Though I have never ran UAS style races, I have definately had the itch to do so. If I do, it will have a 390/420 of some kind on it. Way too many setting around the garage to not do so.