I got this lense just before a recent trip to Moab, UT, and I like it quite a bit. The range covers what I use most often, and was light and cheap enough that I wasn't afraid to take it into tight spaces while hiking or up on a cliff face climbing. The front element does rotate, but this only matters if you're using a polarizer or a graduated ND filter. All in all, a great little lense. I got mine in EX condition from keh for about 100 dollars.
That being said:
If you're looking for a 'one lense' solution for taking around town, I think it would be a good solution providing it fits the range you use most often, and don't need the 2.8 of the tamron. If you want to supplement or replace the lenses you have now though, you won't gain much, if anything. Maybe half a stop on some focal lengths. I'd go for either the tamron version, or a fixed 50 for the speed.
Quick example of the lense from Arches National Park.