Just my take, but here it is.
I have 7 swivel knives, ranging from really cheap up to a Barry King. I use them all for different things. But except for the one really cheap one I use for the nylon beveling blade, there really isn't enough difference to justify the prices on some of them. Others are going to chime in otherwise, but I've done this for going on 40 years, and if I were to start over again, I'd just get a nice mid-priced one like the old brass one I got at Tandy about 20 years ago.
As for the Al Stohlman round knife, I found I had to thin the angle of the bevel. After that I've had no problems with mine.
As with anything, others will tell you 'this', 'that', but it comes down to what works for you. A good craftsman can do good work with cheap tools, but expensive tools do not guarantee good work. That can only come from you.