Jumped on the TPU bandwagon and got a pair of CYDY (purple) from
eBay. It came with a little o-ring and I saw a specific instruction on one of the Google images that the o-ring should be placed at the base of the valve
inside the rim to prevent rim hole burr from scuffing the valve/tube interface. So I did that, rather than putting the o-ring like a valve nut on a conventional butyl tube with threaded valve.
Air seems to hold when stored, no complete deflation overtime. Maybe 5psi over a week of being left pumped at 70psi off the bike.
Only 46miles since swapping from a cheap butyl (Vavert?) so I can't tell the difference yet. Also swapped to new wheel (P1800) and tyres (Durano Plus) so... I'll never be able to tell the change solely from TPU...