@Equilibrium, usually those services aren't a good idea unless and until you can get dialed in on your review strategy without using third-party software. You'll want to send emails (and/or ask customers in-person) manually, and figure out what works. Otherwise you just automate an approach that doesn't work and burn through all your customers.
Once you have a decent pile of reviews (preferably on several review sites) and just want to make it easier, then you might consider a solution like GatherUp or Grade.us.
A very large electrical/plumbing/HVAC contractor in my area uses PulseM to get reviews. It works great, they are one of those companies that use the strong selling tactics and will upsell a service call to a $12K generator or #15K new HVAC system, yet they have 1,300 reviews and 4.6 stars across Google, BBB, Facebook, etc.
I own a service company and we use nearbynow. They don’t allow for review gating. It’s affordable and can post on location pages based on zip code when adding details to send review. We don’t include yelp because of their guidelines.
New advertising option:
A review of your product or service posted by a Sterling Sky employee. This will also be shared on the Sterling Sky & LSF Twitter accounts, our Facebook group, LinkedIn, and both newsletters.