@ Headley_Grange - have to agree
I have to agree with Headley_Grange here. I have a 540 (upon which el Reg says the 550 is based - no surprise really), and on paper it looks like a good bit of kit. However, I have had plenty of problems with it being unable to connect to the server, random reboots, failure to acquire a satellite lock from time to time. My favourite, is that, when I'm sitting in the carpark at work (the Sat Nav even shows me positioned in the road), It will usually tell me "no route found" to anywhere, until I drive off a few tens of yards, and try again.
IQ Routes does not appear all that it is cracked up to be to me. "Drive like a local" they say! Yeah, right. The planning appers to favour main roads, and I often find myself ignoring instructions and using a couple of local roads, which I'm pretty sure are quicker.
Also agree that TT customer service is utter, utter pants! Their standard advice to every problem seems to be to reset everything (by various means), which causes loss of carefully entered settings, favourites, and so on. The advice to set your favourites as POIs instead does appear to be the best way to do it, but I even lost those once! My first point of call for service and support is NOT TT customer services, it is a fairly well known independent GPS forum, and I find the advice I get from them to be considerably more convincing, reassuring, and successful than TT's own customer service department.
Having actually bought a 540, I'll stick with it (don't have much choice really, unless I want to fork out more money on something else, and the 540 does work well enough most of the time), but I'd think very carefully about buying a SatNav descended from the 540 in the future, and I'd probably try something else instead.