I run a single GPS for the whole session, then split the file afterwards. In practice, about 99% of the time I foil first, so I upload the first split as foil, and I upload the full, uncut file as fin. That doesn't create any issues for GPSTC, because I'm still consistently faster on fin than foil across all disciplines. Total distance is rarely more than ~60 km anyway, even if the session is all fin or all foil.
I haven't had any issues with windsurfing (tough wood), but with windfoiling I've had some massive crashes... I've since invested in one of these harness release hooks, it's helped send me away from the gear when crashing
While I still love getting out on the fin, these days GPS-wise, I feel like I've got more to work on with the foil in that 8-18 knot range than I do on a fin. That said, if I rock up late to Wello and it's already blowing 15-18 knots, I'll usually grab the fin because it's quicker to get on the water. If I'm there earlier and the wind builds through the day, I'll generally just step down in wing or sail size on the foil since it's already rigged. Also this is all tide dependent as well...
