Not a writer but a gunsmith... - I have both a Teslong & a Hawkeye.
For fine work I use the Hawkeye (over a grand), and I use the Teslong to take pictures for people more than anything else.
So if you are machining I would say you want the Hawkeye, but for general fun of he mill inspection stuff he 50 dollar Teslong is fine
This^^^^
Will also note that when most shooters buy borescope, they're often disappointed with the insides of their rifle barrels--partly because of how often there's relatively little correlation between how a bore looks, and how well it shoots. But there are plenty of other uses that make them worthwhile.
