We tried Tabcat and were VERY unimpressed - returned it for a refund in the end because it failed to detect our cat even when he was in the same room and we were pointing the detector right at him!
Had a look on Amazon and were put off many brands by the fact that they had obviously paid for a number of lengthy and slavishly positive reviews - this makes me distrust the brands.
Most trackers are really designed for dogs and would be unsuitable for smaller cats - having said which, our (medium to large-sized) cats seem to wear 30g trackers on their collars without even noticing.
We looked at weight, size, upfront cost, ongoing cost, and battery life. Also looked at whether they came as a collar or as something to put onto a collar. (Our cats tend to pull off quick-release collars very easily, so we wanted something to put onto an elasticated collar.)
We've been using Pod trackers on both our cats for the last few months and have been pleased with them.
The setup seems relatively easy (and I'm not a very techy person). The battery seems to last just over 2 days (approx), but each tracker comes with 2 batteries and a charger, so it's fairly easy to just have the spare battery on to charge and swap them over when you need to. It's also pretty waterproof.
It CAN track your cat constantly in real time, but this would eat the battery life to a ridiculous degree (battery would last a few hours). So we have it set so as to locate the cat on demand. It will do this accurately to within about 5 metres in our experience. It works using your home Wifi, local mobile phone masts, and/or GPS satellites, so it should work pretty much anywhere.
They have a new model of Pod out now which might be worth looking into - I'm a bit concerned about how long our older Pod version will be usable, given changes in mobile phone network coverage.
Hope this may be helpful!