The reviews have gotten more in-depth and of more expensive items as he's gotten more popular over the years, which has likely given him the ability to do more frequent and expensive reviews.

On the farm part, there's a pretty funny video he has called (iirc) "Does Project Farm actually farm?"

2.5m subscribers is nothing to sneeze at if they have ads enabled.

He has stepped up to approximately one per week. That's the point at which a popular Youtube channel can be a primary income.

It's coming from Youtube, here's his SocialBlade stats:

https://socialblade.com/youtube/c/@projectfarm

And I expect that he's near the top of those numbers, because his viewers are probably buying expensive tools based on his recommendations rather than an equivalent number of views watching a cartoon for kids or cute animals or something else difficult to market.

At close to a million views on many of his videos, and something like $0.01 per ad view, he's likely making on the order of $10k per video. Buying and destructively testing some shop vacs, hose clamps, or whatever is just part of that budget.

I always wonder this with engineering channels. Where are these people getting thousands of pounds for each project? It must really cut into their earnings.