Not a fan of that. Too low, and a 20 second reload is way too low for anything that isn't going to be one shotting stuff.
The problem is that there is only one mark of OMD and it can seed anywhere.
So the player will be attacking the OMD with both an early game fleet and a late game fleet.
You run into a system with an OMD only 3 hops out from your homeworld and you have to take it, so we are in the early game.
There are OMDs on the Core/Homeworlds that you have to deal with (late-game).
How do we make the OMD a threat, but not a stonewall in both these situations?
My answer is high damage on a slow ROF attack. This allows the attack to be high enough damage to be a threat to starships in the late game but a slow enough ROF that you are not wiping an early game starship fleet out in seconds.
If it did not open up too many options for cheesing (notably with transports) I'd suggest an even higher damage with slower ROF attack for the OMD.
If you boost the damage on the 20 second attack you are one-shotting every starship available in the early game and stonewalling the player.
If you lower the damage and increase the attack speed it is now not powerful enough to be a threat against high mark starships in the late game.
D.