I haven't had any experience with this dolly but I'd say that it's not going to be up to the job, especially in the long term. If you look online, you'll see that most are much more expensive and more heavily built.
If you Google "motorized trailer dolly" you'll get a lot of hits, compare prices, weight and specs and you'll get an idea of why the Vevor seems undersized for the job. Your GVWR is 7,000#. This isn't something you want to skimp on or you risk injury to yourself and/or damage to your trailer.
You'll also notice that none of the vendors selling the Vevor dolly show any more than a handful of reviews.
Having said that, if your trailer has a wheeled tongue jack now, and if you're now able to move it around manually and you'll only be moving it for short distances on flat concrete, it might be OK, at least until it fails.
Personally I had a Powercaster dolly which start at about $2,000, that I bought used. They're built like tanks and I sold it for $600 on Craigslist when I moved from a TT to a MH. Power Caster has a classifieds page with used units for sale by owners:
Power Caster Bravenet Classifieds -
I would think that, with all the trailer boats in your area, there has to be something more suitable not too far away on Craigslist for a reasonable price.