When choosing a product, it often does come down to trust in the team that built it.
Still, the product itself, the pricing, and whether/how it serves your goals--these all matter. If you're going to build business on top of any of these services, you probably want a bit more than a gut feeling when choosing one.
Rather than weigh in on which solution is best--since I am obviously biased and could obviously take the other guys in an arm-wrestle

--let me offer a little bit of a framework to help evaluate solutions like Grade.us and GetFiveStars.
If you're in the market, these two are both worth a look. But there are lots of fly-by-nights with apparently equal services that can be summarily eliminated with a little probing.
I think it helps to identify your broad review-related goals, like
Review Acquisition or
Review Monitoring/Amplification. Then start asking what tools and tactics that are going to best serve those goals for you/your clients.
Review Acquisition
- Does the tool support collecting reviews on *all* of your target review sites?
- Can you automate review request campaigns? Can they be triggered by the customer? By the client? By an API?
- Does the tool support extending campaigns in email? SMS? Print? Embeddable widgets? Email signatures?
- Does the tool prioritize getting reviews where you need them?
- Can you segment happy vs. unhappy customers and guide the customer accordingly?
- Is the process easy, inviting, well-designed, mobile-friendly, not sleazy?
- Is the tool customizable?
- Can it be white-labeled?
Review Monitoring/Amplification
- Does the tool monitor all of your target review sites?
- Does it capture all past, present and future reviews, or just select reviews from third-party APIs?
- Does coverage includes major, minor and industry-specific sites?
- Will you receive alerts when new reviews are published anywhere?
- Can you auto-publish positive reviews to your website? Via HTML/JavaScript? Via Wordpress plugin? Via Joomla module?
- Can the system auto-share positive reviews to social media? With an image of the review for a more engaging post?
- Can you control the criteria for review re-publishing as well as override these settings as needed?
- Are the reviews published for SEO in your choice of rich-snippet markup?
- Does the tool provide you and your client PDF and web-based performance/trend reports so that you/they know your ROI?
- Can reports be generated on an arbitrary recurring schedule and sent automatically? Can they be white-labeled? Can they aggregate data for large multi-location businesses?
- Is there an API available for the review data?
There are lots more questions to ask, too. And by all means, do take your vendors to task with them. That's what we're here for...