After testing these 2 pedals for a couple of weeks, I can only say that you as a player will be the winner. Both pedals sound very good but are very different as well. As a team, they can get you a huge amount of killer tones. Whatever pedal you decide to buy, you will get a top of the line pedal for sure!
Both the RR Amps FatDrive and the GuitarSystems DriveTool are related to a certain sought after pedal but they take things into a different direction. The FatDrive stays closer to the original but were the original works best as a transparent booster, the FatDrive also sounds great as a standalone OD. It can kick any amp into that smooth chewy compression that is very rewarding to play. It can be very transparent and although it only has a treble control, it provides plenty of tweakability.
The DriveTool is the love-child of 2 well known pedals with a very different outcome. It can be used as a booster but works better as a drive pedal in my opinion. Tonally, it definitely reminds me of the Red Lama that it is based on but with a couple of twists. The result is a very dynamic and in your face tone that takes no prisoners.When playing alone, I struggled dialing it in but take it to a band/live-situation and it comes alive. With this pedal, you WILL stand out in the mix so you better get your act together!
I will be posting more in depth reviews of each pedal on effectsdatabase.com in a few days.