The AIM Sports Inc Extended HK91/G3 M-Lok Hand guard should work with the 16" model PTR 91.
The AIM Sports Inc Extended HK91/G3 M-Lok Hand guard is not compatible with the Sig M400 Tread. Your Tread fits standard AR15 handguards.
The AIM Sports Inc Extended HK91/G3 M-Lok Hand guard is wider than model MMH92.
The AIM Sports Inc Extended HK91/G3 M-Lok Hand guard will not work with the Cetme 308.
AIM Sports does not state where the AIM Sports Inc Extended HK91/G3 M-Lok Hand guard is made. For that information I recommend contacting AIM Sports.
The AIM Sports Inc Extended HK91/G3 M-Lok Hand guard fits with most HK91/G3 variants and should fit with your FA-91 Clone. Although minor modification/fitting may be required.
The AIM Sports Inc Extended HK91/G3 M-Lok Hand guard might be able to fit your CETME L. The handguard is supposed to be compatible with the G3 and its variants/clones. I cannot guarantee fitment and would recommend reaching out to AIM Sports directly for compatibility confirmation. You can find their contact information below:
https://www.aimsportsinc.com/contact/
No, this will not work with most airsoft models.
No, this handguard will not work with any AR platform rifle like the M&P 15 Sport.
All the manufacturer states is: Compatible with most HK91/G3 variants.