It’s better than nothing but the plates are in an awkward place IMO. Also consider you are likely to be picking up your bodyweight in each hand and I don’t know how well straps would deal with that (especially if they begin spinning). You also wont experience the “rocking” that you can get on farmers handles which can be off putting if it hasn’t happened to you before.
But like I said, better than nothing and almost certainly better than DBs and if you can get some practice with the real deal you’ll probably be okay.
That said, if there is a turn in your event then it’s an entirely new ball game.
Damn, I can’t even imagine how that works? You’ll probably find a home made axle is cheaper than fat gripz BTW.