The main ones seem to be Pawfit and Tractive. I currently use Pawfit but find that their Pawfit 3 trackers have some issues at times. I've gone through a number of replacements in the past year, all under warranty.
Was looking at Tractive but their upfront subscription fee of at least two years (apparently non refundable after 30 days) isn't appealing.
Pawfit's customer service via email is very good.
How good (or bad) is Tractive's customer support for UK residents? Do they have any UK contacts? From what I've seen so far it's all US-based and reviews are poor.
Also, if you use another type of tracker, do you have any recommendations?
Is there even a good GPS-based tracker which you pay for upfront with no monthly subscription?