I am impressed...
Mixmaster looks to be an extensive custom job, while the other 5 are probably only modified to combine. But saying that, to make them combine and creating the Devastator parts as well would have taken a very long time to do. Not to mention painting them all, which probably required some disassembly as well.

I wonder how many hours it all took, so that we can see what the 'hourly rate' ended up being...