I don't have any first hand experience on the matter, but have also been looking into the subject of fixed blade, replaceable blades and mechanical blades.
The main advantage I hear for mechanical blades is they are more likely to fly like your field tips. The disadvantage being if you hit bone or if you hit the deer on an odd angle, you won't get the penetration you need. I think this goes with tips that have replaceable blades as well.
Fixed blades are just the reverse in advantages/disadvantages. There is a good chance changing over from field tips to fixed blade broadheads, you will need to adjust your sights. From what I read though it's hard to beat a fixed blade broad head w/ blade all the way to the tip for penetration.
Again, not first hand experience... its just what the internet told me and sometimes the internet tells different people different things. Nothing beats actual experience. I will know how my broadheads fly vs the field tips on my bow next weekend.