One issue for both kits is the mount for the Flakvierling. PMMS says the Dragon one is accurate while the Tumpeter one is not. In fact neither are really correct. Having looked at a number of pictures the mount had a number of legs on them which to further cloud things looks to have been modified in the field. In the picture below it appears that the crew has attached a vertical set of legs to the angled leg coming from the bottom of gun. I suspect this was to give it more height and and a clearer field of fire.
Now having said all this which one to use. I could scratch build a mount but I ain't interested in this option. Besides who in the hell is going to really bitch about the mount unless one is a fanatical Follower of this type of vehicle and even then the mounts varied from one vehicle to another.One straight forward option is I can just use the Trumpeter kit part. Funny thing about the Trumpy part is that its very similar to the mount on the old Tamiya 7/1 Flakvierling. Also, I have a picture showing what looks like a close match to this mount. see below.
Similar to the Trumpeter mount