I have a tacx flux, they are unreliable but the faults are usually traced back to the belt. Im on my third flux (previous two replaced under warranty) and when the belt failed on this one I just bought a new belt from eBay rather than take it back again. It’s an easy swap and is now working well.
Depending on model it will only work with 130/135mm qr hubs and a long cage mech might hit the feet when shifting into bigger gears
Edit: when it’s working it is a perfectly fine trainer, connects to TR ok and gives stable fairly accurate power. It reads close to my 4iiii pm at lower wattages but is about 10 W lower at higher ranges. I use two different FTP settings for indoors and outdoors as a result.
Final word, they are going for crazy money on eBay, so £300 is OK in the current market. Definitely worth a punt