I use a Suunto watch (Ambit 3 Peak) which synchs with TP. I don’t have experience using other watches/apps.
Is it seamless? Sort-of. There are some minor issues such as date occasionally differing between Suunto’s (mobile) app and TP, and length of workout differing between Suunto and TP.
I would also note that TP has a relatively small number of recognised sport/workout categories compared to Suunto. In TP, I went to User / Settings / Layout / Quick Views to configure what metrics I want to see – and to be able to modify – for each category of workout (e.g. so you can apply Uphill Athlete’s modifications to TSS for strength workouts).
Not sure I would recommend Suunto though my reasons for saying that have nothing to do with their TP integration and everything to do with the reliability of their HRM and their (lack of) customer service.