So, I've been using the advertised service for a month now. Here are my observations and review.
We have selected 5 keywords for organic visits. OP offered us soft-start of the campaign and recommended adding naked URL as one additional keyword.
Everything was smooth, and
our web-site had been receiving 50+ GSC-recorded visits every day. Most of the visitors were from USA (60%), significant portions from Netherlands and Israel (10% + 10%), and the rest - from all over the world. It was confirmed by Apache log file analysis, and it was clear that visitors spent from 30 seconds to 5 minutes on our site, making 3-25 clicks. Almost all the visitors were PC users with a negligible fraction of mobile device users.
According to GSC, the number of clicks was increased a little bit (ahead of the campaign), and the number of impressions was raised significantly. By the end of the month GSC shows commercial queries in the top of KW list (leading with naked URL). Our curse with the 'free' prefix disappeared.
The most interesting part, our ranking positions were changed, and it happens after ~3 weeks:
KW1 - from 89 to 39 (!)
KW2 - from 91 to 70
KW3 - from 70 to 49
KW4 - from 52 to 35
KW5 - from 53 to 31
It doesn't look like a miracle, but the progress is obvious.
What could be improved:
- the daily number of visitors is fluctuating from 50 to 200 and support said they couldn't fine-tune it. Usually I love overdelivery, but I'm not sure whether it's acceptable in this case

- no real-time stats, you can only monitor GSC with 2-day delay
Overall, I like the service and
signed up for the next month.
Recommended.