I'm realizing I never returned to post my Spark results. Bottom line: much prefer the Fulltone Fat Boost 1. Despite the hype/advertising, the Spark had a "compressed" sound/feel to me whereas the Fat Boost sounds/feels more "open." Not a knock per se on the Spark - it may be perfect for your app - but wasn't what I was seeking. At this point, having A-B'd in person the Fat Boost 1 with several good boost pedals (or pedals that can be used for a boost), including the Earth Drive, I'm confident the Fat Boost 1 is for me and will not be searching further in this vein.
Disclaimers: I'm happy to share whatever relevant gear knowledge or experience I have. Genuflection/payment/proof of worthiness neither sought nor accepted. I don't design, build, market, sell or endorse for pay any new music product or service. I occasionally sell personal used gear. I am an unpaid endorser of SoundScaper Productions and Godfrey Daniels Guitarworks.