I've made a living using ladders and have a large variety still. I have jacks, planks, levelers and stand off's'. I have A frames from 2' to 8' and extensions from 14' (they call them 16) to 34' which I can no longer even stand up.
I have never been tempted to buy a combo ladder. However, they are a good idea for someone who needs something compact, versatile and portable w/o a big rack. Sometimes I see termite inspectors with those multi ladders but I've never seen a roofer with one.
To me, having a number of safe planks has given me more options than ladders alone. A quick look at
this page will give you plenty of ideas.