I can't comment much on .43 as I have not used it
It was reasonably popular among pistol players a couple of years ago.
.43 suffers slightly from being a non standard calibre. This can mean you are not able to use it, eg when events are site or trader paint only
Also clear paint events. I believe you can get .43 clear but this paint does vary and for the types of sites that go for clear paint events you will often not be allowed to bring your own as it does vary considerably with good and bad or terrible batches and degradability
With all that though you can always ask an organizer, and with some events some traders may be willing to bring .43 for you
You may also be able to ask about velocities, you might need to stick to the same velocity or may be allowed a different velocity due to the lower mass
Also people I've seen have been happy with their .43 pistols
As a .68 alternate the Tpx can take a FS capable breach and compatible magazines are available or standard ones can be modified
This is of course dependant on your opinion on the pistol size. It's about the same overall size but the grip is less fat