I have a TPU case from eBay - similar to the Belkin; perhaps a bit thinner - and I have no problem using it w/ the Kensington sleeve. I suppose you could say it's a tight fit but IMHO, that's how neoprene is supposed to fit. And I don't have a problem with the TPU sticking to the neoprene when sliding it In and out (as a previous poster mentioned). I also have a $3 neoprene case (from Meritline) that fits a lot looser but I don't like it nearly as much.