this is not realy an answer rather than an opinion:
First, for D-Tuna
to work, you'll need to put your bridge in Dive Bomb only, so you'll lose the "full floating" anyway. You can either use a block of wood, a stock of pennies or a Tremol-no (or something similar)
Second, when this is done, you'll be able to go from E to D either with the fine tuner (you'll have to set it down to E when the fine tuner is almost tight) or unlock the string lock and do it with regular tuner.
When you get the trick and get used to going from E to D and vice-versa, you won't need any device to do it for you. It can be done realy quick:
To drop to D, hit the 4th string (D String) and tune accordingly
To rise to E, hit the 1st (high E) and tune accordingly.
This way, you'll save the dough for the bridge (Even a floyd rose special won't go for under 75$), and for the D-Tuna (around 50$)