As many other people mentioned here, the difference is the price point.
Not everyone wants to pay $80-$100 for a Godzilla toy, no matter how many points of articulation that it has. Sure, collectors do pay that. But Neca is not targeting the same niche market that SH Monster Arts figures appeal to. There will be some overlapping of markets, but the niche Neca are going to fill is *exactly* the niche that SHMA cannot fill: the market of affordably priced Godzilla toys that anyone who just saw the film can pick up.
Bandai has already started exploiting that market here in the US, so they will be NECA's main competition, not SH Monster Arts. Directly comparing Neca with SHMA is insane, of course Neca's figures won't be as highly detailed/articulated/etc. But, they also won't cost more than? $25 or whatever the MSRP is pegged at right now.
Now, we might get some of their super-detailed 18-inch figures for Godzilla, like they did with Pacific Rim. Those would be pretty cool too, and probably stand up well to SHMA in direct comparison. I hope we do see some -- for me, all Godzilla toys are welcome
The more the merrier!
EDIT: to say, Whoa... MekaGojira3k .... your signature gif is *the* most spectacular thing perhaps in the history of spectacular things!
So. Awesome.
"...WILL. IT. WORK?"