It's been mentioned here before. It's hard enough to make wood burn cleanly in a small stove like that, so to get it to burn cleanly AND take serious amounts of energy from it for generating electricity is going to be really tough. My view is that I'd want to hear some positive experience before even considering buying one, and I personally wouldn't buy one.
I've looked into ThermoElectric Generators off and on over the decades and I've seen a number of products which are advertised but never actually seem to become available. I've come to the conclusion that until large numbers of production motor vehicles which use them in their exhaust systems start finding their way onto the world's scrap heaps it's not going to happen. The generators are starting to go into production now, so it will be a few years yet -- if it works.