I wouldn’t buy one for small boiler work. In fact I wouldn’t buy one for any purpose; they’re terrible value for money and the tiny oxygen supply will be gone in a quarter of the time it takes to use up the fuel gas (assuming it’s not acetylene, which it won’t be, in the UK at any rate).
If you think you’ll need oxy-fuel equipment in the longer term, secondhand, good-as-new oxy-fuel set-ups, often with a range of nozzles, can be had for very little money. For small to medium work, a secondhand oxygen concentrator will supply your O2 needs.