I’ve also owned – in approximate order of personal preference – a Sputnik Quad VCF/VCA, Dopefer A-101-2, Dynamic Impulse Filter, DPLPG, Gerridae, and 0HP Vactrol LPG.
Natural Gate is the best of them for sound, playability and controllability
(I loved the sound of the Sputnik, and find the Doepfer is quite controllable. I liked DPLPG’s sound quite a bit but it didn’t work well for slow attacks or quieter CVs beneath a certain threshold.)
I got to try it with a Mangrove at KnobCon last year and was impressed by it more than anything else at the show. When it became available for sale, there was only a 7 minute gap between the timestamp on the announcement and the email confirming my purchase 
I’ve got a CV.OCD which provides 12 assignable gate/trigger/clock outputs along with 4 CVs. As far as controlling the future ER-301 goes, there are a few options that look good. FH-1 is a possibility, but there are some others too… I probably can’t go wrong with any of them but I’ll hold off on my decision for now.