I started using modelers when I could make them just as loud as my tube amps and annoy everyone else in the band.
RIght now I use both. I have a Quad Cortex, a helix rack and also a Helix HX Stomp XL. I use a line 6 monitor and can get it to sound like a real amp.
When touring, I would use my Helix rack for FX along with a tube amp. The great thing is that if the amp goes down, I have the Helix amp models to use. On smaller gigs I use a tube amp with the Stomp XL for FX and again as a back up.
so:
1) Portable.....yep the modelers fit in really small little cases
2) Reliability......I have had the Line 6 stuff for over 10 years without any problems and do not see them as disposable at all. I think some of the Boss Katana kind of stuff can be seen that way, but the high end stuff is not.
3) price is no comparison as you comapre one amp with the shitload of amps that you get in the Line 6, QC or Fractal, etc. stuff. So I have Orange, Fender, Marshall , Dumble, Hi-Watt, Dr. Z, etc. all in one box that costs a lot less than a boutique amp with the QC and better Helix stuff around $1600-1800. It has been nice to switch from a deluxe or Princeton to a big ass Marshall sound mid song.
4) Flexibility....Yeah, the right tube amp and pedals is pretty cool. But with the better modelers, you have a zillion amps and pedals all built in. I don't think my old ears can tell the difference between an original Klon or Tube Screamer and a modeled one. The Lexicon reverbs are steller and all digital and have been the studio go to for years. I believe that Eric Johnson can tell the differences in this stuff but not me.
5) Sound great for sure. There is something magical about my tube amps but now there is something equally magical about modelers in a different way. The line 6 powercab+ is pretty cooland has all sorts of flexibility. I use mine for acoustic gigs as well as electric. The QC has models of famous mic preamps and lately I have been playing gigs 50/50 acoustic/electric. I can get a killer acoustic soundusing the acoustic speaker model and thne swithc to a Deluxe model witha Creamback all in the same box.
I will never give up my tubes but I am becoming more and more satisified with the modeled stuff.