And those magnets would explain why mech flamers are so heavy.
Aye! But I think a heat gun effect would honestly be more scary, because unless you've got Thermal vision stuff active, you don't see it. Its just a wall of heat well in excess of 2000c that washes over part of your squad, all but vaporising the poor sods caught in it. There might well be a 'flame' but it would be round the muzzle, and more akin to a fighters afterburner.
A heatgun effect would basically be this -
https://www.youtube.com/watch?v=aEJQpwZ0pp0&fbclid=IwAR07t2PYB7GAJ6Vi1Jsf3Y8fdYgHWfJT8zYXGx7cW3HM2Wp4dy-xyaa6K40 just a LOT faster and hotter.
A heavy flamer is a more traditional version of the flamethrower, it has a fuel source and propels it that way, but that would also be nasty. First we're instinctively afraid of fire, and second it still burns HELLA hot, god knows what they use as a fuel for it but nasty stuff. And its harder to avoid because this burning stuff its spraying splashes everywhere. And its effects are also probably worse. You could probably hide from a 'heat gun' type flamer if you had some solid enough cover to get behind. And it probably only fires for a really short time. A heavy flamer's gel is going to stick to what it hits, and keep on burning, they could use gellied liquid oxygen and magnesium or some other nasty compound mixes. A flame gun is going to char what it hits even if exposed for a heartbeat. A heavy flamer would be more like that scene from Starship troopers where that soldier gets her arm caught by a tanker bug's fire.