They’re pretty good - ProMag Polymer Steel Sig Sauer P320 9mm 21-Round Pistol Magazine

Look and perform almost identical to SIG brand. My one negative is that are hard to load once you get to the 20-21st mag but I’m sure throughout time as the spring gets worked it’ll get better. Other than that the perform phenomenally and 100% better since they’re $20 instead of $50 like the SIG ones