While I know nothing at all about Timpdon, lots of people on this board, including me, use Cliff Barker's stuff which operates in the 433 MHz band. With his FM kit I have never experienced any glitching (have occasionally around two 10,000 litre metal water tanks with the AM version but even there it is not a significant problem); nor have I had interference with other operators or between my locos. I do like the fact that there is no need for continuous comms between tx and rx; and the size of the tx which fit in you pocket - I use both types although I prefer the keyfob.
Steve