For sub-sonic rounds a standard carbine weight buffer is recommended.
That guy is wrong, wrong. Suppressed short barrel, actually, any suppressed should use a H buffer. Preferably a H2 or possibly H3.
If you are shooting those subsonic rounds suppressed I would go with a H2 buffer
I just spoke with the folks at Sprinco Recoil Solutions regarding this very situation. I have a 10.5" barrel .223 MilSpec bolt, carbine gas system, tube, spring and buffer which is currently ejecting in the 1:30-2:00. I will eventually be suppressing it (I know, I know) so it will get a adjustable gas block then. They suggested one of their Orange springs with an H3 buffer. That is their heaviest spring. Tests seem to indicate a heavier spring with a lighter buffer tends to give better reliability.