I have built four of the Italeri Kits and can say that they are an excellent kit to build. The lower hull has not changed from Italeri's earlier M109 kit and still has the flotation kit molded onto the lower hull. I have yet to see and M109A6 with this and it could be removed and filled in. The turret does do a nice job of covering this up and if you leave off the air hose connections you will not see them too much as long as the turret is not turned.
With a little hard work and dry fitting the travel lock can be fully functional. Pay very close attention to mounting the gun tube to the turret. I had to shim it on all of them to get the correct placement. Also, the front left corner needs some strip stryene to fill in a gap forward of the battery compartment. The air vent on the turrets front left door needs to be re-worked to have bolt heads in an offset triangulat pattern to the rim. The instructions for the headlights are wrong. They should be painted the same way on each side (headlight on the left, when facing the front, and the blackout drive light is on the right). I replaced the kit supplied mantlet cover with one made from tissue paper so that the gun could be elevated.
I have a few more notes lying around but am not sure of Revell is using the same instruction sheet or folows the same part numbers. If it does, I can tell you what I modified, left off or what not.
Skybow makes a really nice set of tracks for the M109 family and if you can find one, it will make a nice addition to the kit!
I have pictures of each one, but have not yet figured out how to post them here. Good luck on your build!