I've been using SERP Watch for just a few hours now. I've been looking for a good keyword ranking tool and so far, I'm quite happy with the deal.

What it does well:
SERP Watch so far seems a very competent keyword tracker. For any keywords you want to watch, you can easily input them into SERP Watch and get very relevant data.
I like how I can click a single button and see the results as SERP Watch sees them. This already helped me identify an issue on my search results (Google was replacing my meta-descriptions with their own, which means I need to do a better job of creating these).

What it doesn't do well:
SERP Watch is not really a keyword discovery tool. You can input a keyword and ask for related suggestions, but it gave very few suggestions and they weren't very good.
Unlike tools like Ahrefs, which has a giant index and can tell you keywords that you're ranking for that you didn't know about, SERP Watch will only track the keywords that you tell it to look for.
I connected my Google Analytics account hoping it could auto-populate my keywords from there, but it won't do that. You can only input keywords manually or via csv.
Not a huge fan of the notification settings. I just want a good weekly update on my keywords, but it only gave me options for hourly or daily (another review mentioned it could give clients a weekly email. Maybe I need to become my own client?)

Overall, I'm happy with the tool. It's definitely not on par with Ahrefs, Moz.com or the other top tools out there. However, my own needs are small enough that I haven't wanted to pay for those services, so I've been very happy to find this LTD that gives me most of the functionality I want.