It was kind of scary since it was about a 1/2 hour ride or more and was not "affiliated" with the cruise. The outfit itself was a bit ...shall we say...off the beaten path and looking kind of neglected. However...the ride itself was great. Some additional feedback for you:
1) Ask if they use western saddles. Ours were not and are much harder to ride.
2) The "ride in the water" was OK with this outfit. One by one the guide leads you and a horse through a small lagoon for about a minute. I passed, but my kids kind of enjoyed it.
3) We had to tip both the guide AND the taxi driver since they were with two different companies.
I would do it again...but perhaps shop a bit more next time.
RCL Liberty in 2008
Princess cruise in 2001
Costa cruise in 1989