That would be great to get some 146 time if you can. Why not? The aircraft will likely be gone in a few years and at least you would have some experience on it... Sounds like a great deal and I would enjoy it very much.
From what I hear, the Dash 8-400 performs as well if not better than the 146 anyway - you won't notice much difference except for the full glass cockpit vs. the round dials... At least you will have 146 time - that would be great to have...