I've only seen one (the underswap one I think) and I guess it's a pretty neat idea for those who like it but I'm not into AUs much myself (I do kiiiind of like Underswap and some smaller AUs that are more like headcanons but I don't care for most of them)

I'm pretty sure I won't play any of them, I think nothing will really beat the original. Though I kinda want to play the Underswap Omega Temmie xD