Believe me, on average, it's half day work.
It works type of reviews will take few minutes but that's not a review.
If it's a decent review, you have to do this at least:
Take video, photos of the product.
Edit, comment, point features etc... upload, post links.
This one step takes few hours right there and it's just a start.
Then comes the real thing.
Explain features, settings, mounting options etc...
Compare physically with other dashcams.
Compare videos with others. Again editing videos, watching and listening to make sure there's no audio that you don't want to have like phone calls etc... takes few more hours.
Taking screen shots from interesting points in the videos, explaining them...
Driving around at different times for day vs night etc...
Following up on the thread/review when someone comments or asks questions...
For specific cameras with features like wi-fi, waterproof etc... need to set up to test them.
And the list goes on...
It's fun to start when it's your 1st camera or if you plan on posting one line review otherwise takes a lots of time.
I have reviewed many as it's kinda hobby and few were complete waste of time as the products were of poor quality and so unusable that I can't even give them to friends while few are really nice that I keep in car even when I have multiple dashcams.
Maybe better than asking "who wants free for review" is to setup a giveaway at social sites or contact amazon vine reviewers and don't force to write glowing reviews even if it's bad as others will buy it and if it turns out to be not what the reviews say, you'll have issues dealing with returns as well as they can complain amazon for fake reviews.
Dang this post took more than half hour on my phone and it's not even a review.
Buyers nowadays only buy products with good reviews so new seller/product needs to do what needs to be done to sell products, whether by giving free or coupons or even pay to have reviews.
That's the reality.