Hi Shaun. I also believe that it's ethical.
But, it's also pretty straightforward to generate 20 leads per month via adwords.
The true value or otherwise of this service will be in the actual paid cost per lead. If they can actually provide these leads at a saving compared to running your won adwords account or as opposed to paying a small management fee to one of many adwords companies, then it has some merit.
Although, in my opinion, there is a potential problem and a disconnect between the website and therefore company, that the customer initially makes contact with, and the company (your business) who follows up on the lead. There's certainly a chance of confusion and a potential of the lead running scared.
It does appear a targeted form of adwords management. If I'm wrong, Oliver, please correct me.