I've got the Big Dot (tritrium) on a Kimber Ultra Carry and I really like them. They're very fast to acquire - just put the front sight on the target, line it up in the vee and squeeze. Bear in mind that they are COMBAT sights, not target sights
In all honesty, it took a little practive to get used to (i.e. about an hour and a box & a half of hardball), but my accuracy out to 25' is just fine (POI=POA at that distance), I can hold a group under 4" pretty consistently. For a CQB pistol, that works for me.
I've always thought the Ultra Carry was quite accurate for such a short snort, and the Ashleys haven't hurt a bit. YMMV, but try 'em, you'll like 'em