One MKB-TS owner here who's now taking a second look at The Legacy MODs. I may have chosen differently if I knew there was a flat top for the Legacy available. The Legacy devices, at there current retail price, make the MKB look overpriced.
My MKB needed significant modding to work as it should. The only support base available has been ECF. The US venders selling the MKB can only support up to the point the manufacturer stands behind the product. There are at least two versions of the MKB out there now. The second version comes with a gold plated spring. The first version has a floating center pin and the second one does not. So you run the risk of not knowing what you'll get if you order one. In my experience an adjustable center pin is %100 necessary because all the atty's out there differ.
As far as I know the MKB's in-stock at US venders right now are the first version. Get 'em while you can but know you will have to fix some stuff. I would not get the second version despite it's improved switch, due to the fixed center pin in the 510 connection. Rainbow Heaven doesn't seem to know EXACTLY what they are trying to accomplish.
The Legacy devices are US design, build, and support. So if you ever need anything for your legacy, YOU WILL BE CARED FOR. It's one of the only US mods that has a strong following in Europe. Cloud 9 sells them alongside GG's. If that crowd accepts them, they must be quality. The creators of The Legacy are members of the ECF and can be reached here.
Considering all the CO-OP activity around the MKB, I would guess it's current retail price won't hold much longer. I've lost some good money buying e-cig gear too hastily. Everything is getting better as time passes, so there is no harm in waiting until your %100 sure you want something.