What is the latest policy on using these 3rd party Review solicitation services?

I understand Amazon's policy of not "harassing" customers - and that we're only allowed to ask for a review one time. These 3rd party services offer a way to "automate" clicking the "Request Review", although they send their own email template, etc. The biggest "value-add" they offer is being a little more smart about when they send the Review Request, and perhaps being able to reach a few people that might otherwise not receive a Review email.

G2G or steer clear?