If I'd gone for the P3, I'd have gone for the Exact cart option.
As it is, I'm getting the P6 with Exact cart.
Unfortunately, if I want to play LPs, I need a cart at some point. So I may as well get a good one designed for Rega tables, pre fitted happily at the factory or dealer.
Nothing is perfect, and yes, there will always be the chance of finding something better.
But, do I take the TT home, plug it in and play it. Or:
Take it home with no cart, spend possibly weeks searching, hoping I find something that sounds better to me (never a guarantee), spending quite a few pounds in fuel in the mean time. Then have the hassle of fitting a cart that is possibly a different height to the Rega carts, leaving the arm at a suboptimal angle.
Remembering again, that even this cart wouldn't be perfect.
I'm not convinced it is worth it. Unless the Rega carts are absolutely rubbish, which I don't believe they are.