Personally, I do not like that Happy Limo includes at 20% gratuity in their price. While I will gladly tip 20% if I am pleased with the service, I don't like that it is paid for even if the service is poor.
We actually did not have a good experience with Happy Limo the one time we used them (which was also our first time to use a towncar service). If you seach the transportation section of this board you will find that all of the big towncar companies are now and again going to have someone that was displeased or when there was a problem. However, what I especially didn't like is that when I contacted Happy Limo after we returned to express my displeasure, including the fact that we nearly missed our flight because they did not show up, I never got a response from Happy Limo. I chalked this up as poor customer service and will not use them again. This and also learning later that there are plenty of other towncar companies that let the customer decide how much they want to tip.