I used the latter and find the SI Link system the best of both worlds IMO. They offer accessories including a couple very nice rail sections and a curved fore grip. So what's a possible solution? Recently I discovered that Strike Industries ( Strike Industries) has an attachment system ( SI Link) that is both Key-Mod and M-Lok compatible, and offers the ease of attachment of the Key-mod system with a 'all-metal' M-Lok-type attachment block. That all being said when I've purchased products recently I've been disappointed when the M-Lok rail system was my only option, and that Keymod accessories are fewer and harder to find. When attached the M-Lok attachment system is solid. The issues I have with the M-Lok attachment system is that I've found that attaching an accessory is much slower, and that the M-Lok attachment bar is made from plastic which could fail easier than metal, and that I've experience interference issues with attaching a M-Lok rail at the gas block location. I personally haven't had a Keymod 'attachment' nut fail, and the accessories are/have remained solidly attached. Some have stated that Key-mod attachment nuts have failed on them.

My opinion is based on having both Keymod and M-Lok handguards. I personally like the Key-Mod system due to my opinion that there are greater mounting options on the rail itself, I think Key-Mod rails are lighter-weight, and have a much faster accessory attachment to the Key-mod rail.

Keymod accessories magpul