I do most my sessions on an IDT, and those who know me will agree that my performance has improved tremendously.... but....this will only be if you have a proper setup. I use the Tacx Flow, was about R4000, then I also have an set program from the Science to Sport which I cycle on doing my training accordingly. What helps is you don't run out of climbs, etc...so you can mantain the pace as the program says due to the tacx have the digital screen to adjust tension by a click of a button showing the gradient of the climb and it is also showing my watt output, cadence, HR, etc...keep track of an ODO as well. Thus I will defenitely recommend it as a base and even though I get bored, having a set program times goes by fast....weekends I still go out on the roads, but besides that it was money well spent.
