We are in Slovenia right now, on a different tour--with REI Adventures. Our guides (we have two, one male and one female, for a group of nine participants) are fantastic. They are professional and attentive, very funny, and kind. We have done some tough hiking in rain/snow and they make it fun and possible. I have come to love this country--so welcoming, and beautiful. There is nothing " undeveloped" about the tourist infrastructure, even in the remote places we have been. It is too bad the RS tour only spends three days here. This is my new favorite country in Europe.
And we are traveling with my sister and her husband, who did an REI of Croatia last year. They loved their guides and the whole experience. Great food, great people, fun adventures.
So I would totally recommend visiting these two countries---but maybe a RS tour is not the best way, given the apparent issues with the guide.