I bought the one on my bike from a decent UK supplier - Rewire Security. I have the TK104 as it has an incredible battery life - not as important if you plan to hardwire - it has the same features as the TK102 type tracker.
I use my own SIM from GiffGaff as the credit never expires and I only use the SMS based tracking/service so there's no monthly/annual fee. It sends me a google maps link to see exactly where the bike is and has a movement/shock sensor which essentially acts as a silent alarm. This alone saved my bike from an attempted theft last year.
Had a look at the advert you've posted and it looks pretty decent