A few of us bought the following
--Leapy recommended--"As there are a load of clones out there sold through eBay I bought mine direct from the original manufacturer Xexun, the only way I felt I could be absolutely sure. You need their TK102. Be very wary of the clones, they're 'iffy'
Xexun don't actually sell to Joe Public direct but they sold me a 'sample' at a US$ rate (and so is subject to the strength, or otherwise, of the pound)
with the request. He was very very helpful. Make sure and get the 12v to 5v converter too if you want to hard wire to the boat battery, otherwise the internal battery only lasts 36-48 hours before needing a re-charge. It comes with a 240v charger and two Li-ion rechargeables. You'll need a PAYG SIM".
I e mailed David at Xexun and took the unit with a mains hard wire, Fitted and works well. Gives you a few options to set and then if moved you will be texted, also a geo fence if you dont want boat outside an area when in use and also a locate text. I have had no problems and David is the correct supplier and not a copy