If you didn't read the shot review of the TC80-N3 from MR
you should habe a look at it here:
Canon TC80-N3It can be used like a simple cable release as it has the same
push (and lockable) button like the RS80-N3. The Batteries
run for years so there is no need to take them out.
The only thing I miss is the functionality to time two consecutive
exposures every x seconds. This means one cannot use mirror
lockup and tell the thing to make an exposure every 5 minutes.
You'll have to tell it to make an exposure every 2,5 minutes so
the mirror goes up after 2,5 min until the actual exposure happens
after another 2,5 minutes. Needless to say that this isn't exactly
saving your batteries.
Did I mention that the build quality of the TC is great? It actually
feels like a tool and not a toy like the RS (its longer, and heavier).
If you get it you wont regret it