I would approach vendors individually, offer to submit some write-ups on spec (free of course) and see how they like your work.
Have a few friends with these arrangements, they are very good writers and ability to succinctly explain technical workings of things, in a way that will appeal to *all learning styles* (visual, audio, kinestetic, etc.) is what makes a good reviewer.
If you are only going to do video
reviews, then best to submit some samples as well. Good lighting, good technique, good practices (like clean fingernails for instance). Best way is to watch some that you think are good and determine WHY they are.
Here was one on rebuilding eroll atties that I thought was good (from a long time ago). Some people like "personalities".....I just happen to like well put together technical videos:
I've watched a number of these eroll ones, and RJs was the absolute most easy to understand, complete, good pace, and fully explanatory.
Or, if you don't want to approach vendors, start putting your
reviews out there, and if they are good, people WILL notice.
You don'tt have to ask permission.