Lots of plumbers use them for soldering copper pipes. I would expect the refill cost to be quiet high, labor you know vs cost of gas. I wouldnt think you could do much cutting with those small O2 bottles though. They might fulfill a small need but personally, I would go for a bit larger O2 like an 80 CF, same size as a scuba tank, still portable but enough gas to do a small repair. That size wouldnt take up much more room than the little tote tanks.
I used to have a small carry set as well as my full size. It was Very handy, but I also ( had available) carried 5 oxygen and 3 acetylene tanks. It’s fantastic for cutting out in the field, but your done in 5 minutes.
Yes, the cost to refill( I had a refrigeration friendly place, that carried a good supply of extra bottles for exchange) is much more,
Although it was quick to exchange.
My brother has a refrigeration business and when sweating copper and changing out lines, fittings etc, prefers these oxy/acet sets.
A friend let me use his once. They empty pretty fast if you do any cutting. They're fine for a little heating. I believe he told me they were about $30 to refill. When I did get an acetylene outfit, I decided to go with a 75³ft acetylene tank and 80³ft oxygen. Those 2 bottles are about $70 to fill. A little over twice the price, but 4 times the oxygen, and 7 times the acetylene. They're still light enough for me to move around without dreading doing it.
Now I'm thinking about going to propane. The only thing that it can't do is weld. That doesn't make me a bit of difference, since I only have good use of one arm. I don't have the motor skills in my left arm to do any TIG or acetylene welding. Seems like that is perfect for me to make the few cuts that I do use a torch for and all the bending I want to do. From my understanding it's slower, but I try not to get in a rush anyway. Tractor Supply here refills propane bottles at $2.39/ gallon. A 20 pound bottle holds a little over 4 gallons. It won't be cheaper than acetylene, because I'll go through a lot more oxygen. But the propane is much more versatile. Cut steel, fry fish, cook a steak, heat bolts, heater in a ground blind, start a bon fire. And that throws the 1/7, 1/10, and 1/15 rules out the window. I figure I'll trade my acetylene tank for another oxygen, CO2, or 75/25.