I personally really disliked the TF series. For many of the reasons that Rob mentioned. The problem is, that if you zoom out and look at it as a product in a huge market of low end products, its pretty good. Lots of expansion options and the Yamaha brand carries a lot of weight.
But, when you compare it to the excellent QL offerings, its always going to fall short. I think the QL stuff is absolutely excellent, and if you are a rental house/organisation that doesn't have to fill riders, there is not a whole lot that can't be done with a QL5. I mean it does 64 inputs to mix + 8 stereos in a package which is small, with entirely customisable fader layout, for sub £10k.
Of course the QL carries a higher price tag than a lot of its competitors, but thats not surprising when its (functionality wise) basically a PM5D (and then some) for a third of the price...