There are members of the Lego community who feel that building with another other type of connecting block is heretical. Lego was the first and we must remain pure. This includes use of third party creations such as Brickarms.
There have been a few people lately in the MFZ community who are testing that orthodoxy.
The first was the ST-57k Sumu by milt69466. It's made mostly from Kreo.
Then the A2b Angelus Type 2 by Rasann/Kastor the Chinchilla.
milt69466 strikes again with the ST-61k Yellow Tiger and others.
This modified Chub with MegaBloks parts -- called the ST-28I Paladin -- by LowestFormofWit looks really sharp.
And finally, combining MegaBloks and Kreo, LowestFormOfWit's NR-31 Vassal.