There's only a marginal difference between reported efficacy of internal vs. external condoms -- about ~3%. That being said, condoms are only as effective as the person using them, and people tend to be less familiar with internal condoms. Because of this, in terms of average actual use, internal condoms are a bit less effective (~6% less). If you want to use an internal condom, just make sure to read the instructions carefully! I also recommend practicing inserting an internal condom before you actually plan to use it for sex, if possible. It will help you familiarize yourself with how it works! We have a great article on how to use both types of condoms that might help: All the Barriers! All the Time!
Let us know if that article is helpful in navigating condom choices