I can't recommend motor mounts because I went with AWR 70d urethane motor mounts and they definitely add/worsen rattles but most are already there just made more apparent and so it just forces you to find and fix them. Even if you fix them all you have vibration that goes to the chassis that the rubber would dampen, but i see it as a complimentary back rub. I'd say the Mazda Competition for more durability over oem or even the MSM mounts, that's just me though.
As far as 'knock offs' go... I don't mind buying one if the price isn't at the sacrifice of a big difference in quality/fitment. Beyond that a even BIGGER concern is customer service...how many other companies like the miata community has is going to give you the great customer service we are spoiled by?
Supporting the vendors for supporting us is a 'win/win' scenario and as long as they continue being active in the community, delivering quality parts and great customer service then I will strive to support them when i can but there are parts I have opted to source else where but they are few and far between beyond buying used parts from fellow enthusiasts.