The biggest downside of Kdenlive is that it does not use the GPU...if you apply any effect to any video, bye bye GPU, it only uses the CPU. This is like trying to climb a hill on a bicycle vs with a motorize vehicle if you were to use the GPU. This is something that will make anyone who does more serious video editing to never use or even try Kdenlive. Using the CPU + proxy clips is fine in Kdenlive, all smooth. But when you export....it takes a long long time.

Despite this I have used Kdenlive for the entire TROM II documentary, over 5h long, and generally it is very good and stable. If they were to implement the GPU usage then it would be a great video editor.