All drain covers must be certified "unblockable, anti-entrapement" per Federal regulations, that's the second part of the split-drain equation.It's my understanding that yes, if I only have one drain, then flat covers are illegal. But since I have 2 drains off the same pipe, then that's not the case? 2 drains = no suction danger, right?
Flat covers, regardless of how many in a pool, are not either, not legal, not manufactured.
Think of two flat covers and two fools playing around and getting stuck.
If you don't think that happens, ask an insurance company. Even ones certified can be defeated. As the expression goes, "You can't fix stupid." There were many stories in trade publications of ones who did so when they first came out.