What is the downside of using GO SMS Pro and / or Handcent?

All I've been seeing about these apps are the positives. I want to know the negatives of using them, apart from me having to install an additional app to do something that the phone can already do by default. I'm looking to using one of the two because of the built in support for backing up SMS and MMS, something that will come in very handy especially since I text often.