I can only speak from my experience; this $18 plastic housed heat gun from amazon is 54 roasts in and I haven't found enough variance from roast to roast to question it's consistency. My guess is the heat gun will be the first thing to break, to your point. When that happens I can opt to buy another one, a more expensive one, or invest in a more professional setup. I am quite sure I've recouped the $18 I put into it even if it broke tomorrow.

When it comes to my hobbies I like to buy cheap first, quality second. If I wear out the cheap one it means I use it frequently enough to justify spending more on the next one. With OP's original question they can definitely raise their potential by buying higher quality and more configurable components; my point is there is a ton of untapped potential with the tools they have already.