I have been using my manual Pentax lenses on my T2i. The adapter I have is quite finicky, but it saves money. I suggest that you download Magic Lantern --->
Magic Lantern Firmware Wiki and install it. It gives you focus peaking/simulated spli-screen during live view to help you focus the manual lenses. Remember that you loose image stabilization. I shoot in Tv and meter through the viewfinder as the aperture is already set. Remember that there is a 1.6x conversion factor.
The easy manual focus/aperture ring is great to use in video, although you don't have image stabilization. If you choose to sell the Pentax lenses, the Tamron 17-50 with or without IS is a nice lens.