How interchangable are parts from different manufacturers?

I'm sure this has been asked, but I don't have strong google-fu tonight...
I have a MadCow Mini DX3 that I built stock, and now want to convert to dual deploy. Madcow sells the tube I need, but is out of stock on the coupler. I can get a 38mm tube and coupler from Discount Rocketry for a great price, but I'm not sure it'll work...anyone ever mix brands (bonus points if it's THESE brands!)? Any tips and tricks to recommend? Thanks in advance!

Madcow and RW and old wildman FG all match up.

LOC cardboard and blue tube "sorta" match up but I do it a lot with success.

Not sure where DR sources from, so can't help you there.

Discount Rocketry (modelrockets.us) is very thorough about providing dimensions on their tubes and couplers. Madcow, not so much; they don't list dimensions for their couplers. But I have been researching all sorts of parts for my OpenRocket add-on parts database (see https://github.com/dbcook/openrocket-database) and have a pretty good idea. The Madcow 38mm tubes are nominally 5 mils larger than the DR tubes (1.635 Madcow vs 1.630 OR). This should mean that the DR coupler should work but will have an extra 5 mils of clearance, which could make it a bit loose, but I think it oughtta be OK.

madcow lists OD and ID now- https://www.madcowrocketry.com/cardboard-2-6x25-5-3-slot/

EDIT, and now I see not for couplers.... Just like you said. D'oh.

You can always order the DR coupler and if it doesn't work, it's a good excuse to spend time waiting on the Madcow coupler by buying the DR BTs and scratch building another rocket. Can't have too many rocket ya know!