Has anybody seen or used one of these

http://www.rockshore.uk.com/tpms---tyresur...1689-p.asp

i have been looking at TPMS a little while ago

but need 6 wheels for when i am towing,(the one you've linked to doesn't have an high enough psi for the caravan tyres) but haven't managed to find anything that comes with a great review, apart from there "own" praises on there one website which will be a little biased

the Tyron one looks good, but its £200 for 2 wheels and nearly the same for another 4 sensors which is a little OTT