East Crane/E&C make some decent kit. They were the original OEM for Specna Arms and are still OEM for a number of manufacturers, as well as their own stuff.
As far as DMR mods go, the reason why most people suggest an SR25 or similar is that they have a V2.5/"V2 long" gearbox - ie one with a longer piston stroke, which means they can cope with the volume requirements of a longer barrel. With more modern hop designs the reliance on long barrels for accuracy has diminished somewhat so the two E&C guns you've listed start to come into their own, despite only having a standard V2 gearbox. I personally have a MK12 which runs around 420fps with an E&C gearbox perfectly fine.
This is the usual resource for advice on building an AEG DMR https://www.airsoftsniperforum.com/threads/the-holy-grail-of-building-your-dmr-aeg.892/ so go have a read.