Mainly it's that askmike's version hasn't been updated (bugfixes, features, or otherwise) in over 8 months. Askmike left and hasn't returned, and hasn't been accepting pull requests or otherwise given anyone commit access to the repo. When I forked gekko a few months ago, I was doing it because I wanted to fix bugs and add features --  One of the main bugs I fixed was related to how the history is stored and used when a history size of greater than 24 hours is used. (askmike's version from 8 months ago had a major bug and can't correctly load history databases if a window of larger than 24 hours is needed)

WARNING: I've only been supporting cex.io automatic reinvestment to buy more GHS. The way I redesigned is for a reinvestment-type "buy and hold" strategy. I've been doing this in my spare time, but the latest version is finally stable and works as intended so I can probably move on to adding other strategies than the current "buy and hold" reinvestment code.

Last difference is that all the changes in my version are AGPL instead of MIT license. Moving forward I'd prefer to keep my fork as AGPL licensed. I really believe in the idea of making sure people have the source code to their trading engine ESPECIALLY in cases where it's hosted as a managed service. (not everyone has the experience or technical knowledge to run and maintain their own server, but that's no excuse to deny them access to audit the changes made to the source code. This is an important feature of the AGPL license which I strongly believe in)