Well FT sells everything, good and bad. An $8 mod from FastTech is not going to be perfect, wether it is authentic or clone. It is going to use parts that warrant the $8 price. But a $50 clone made out of copper (or other quality metal) with good machnining is about reasonable. You can expect that the $50 went in to using some lasting parts. And still save a ton of money when the authentic is $250+. At this pricepoint, the $50 clone could even have more precise machining, better threading, lower voltage drop.
But if any vendor starts selling mods and atties with regular prices of $1 each, or even $0.50 each... this is the kind of purchase to make if you have the need for low quality spare parts.
I don't really want to say the "you get what you pay for", because for that $250 authentic device, you really don't.
But there is a critical threshold where a mod or atty can't be manufactured any cheaper without sacrificing materials used or time spent. The $5 mods and atomizers on FastTech are below that threshold... they can probably be expected to last as long or longer than a pack of cigarettes though. And a pack of cigarettes would cost more than $5 for most people.