Diffuser plates serve two possible purposes: moderating head and/or spreading it. It sounds like your intended purpose is the latter.
Having said that, electric hobs are often the most even choice. Are you finding yours to be uneven? If there's unevenness within the footprint of the hob, the element probably needs replacing. Unfortunately, coils do develop dead spots, and if you have hobs with two nested coils, one can fail entirely. If this is the situation, a conductive diffuser (and/or very thick bottoms) can help, but not a lot.
However, if what you're trying to accomplish is to even out larger cookware on a smaller hob--mismatched--then a diffuser might be helpful.
As far as I know, there aren't specialized diffuser plates for electrics. I think the rec of Bella Copper or similar is a good one for several reasons, not the least of which is that high heat can soften and delaminate aluminum ones. But they do not have handles, so you need to be careful wrangling the flat sheets.
I have a VonChef clad (3mm aluminum core) plate marketed as an induction converter that functions ok as a spreader on small hobs on lower heat. Inexpensive.
