Fly Stimulator
If you are buying a transponder for your new CT, I assume that since it's the cheapest and lightest on the market you're probably looking at the Microair T2000. Do be aware that the importer has never actually bothered to get CAA approval on it and therefore you can't fit it until they do (rumoured to happen sometime in the hopefully-not-too-distant-future on the back of a German JTSO that doesnt exist yet).
My opinion on people selling avionics in the UK that can't legally be fitted you can probably guess.
G