Haste to let you smash, and safety from counterspells
Based on the latest market prices tracked on TCG Stacked, Summon: Choco/Mog is worth about $0.23 USD for a regular copy and $0.39 USD for a foil copy
With this card's "switch out" mechanic, you'd be able to cycle through your different Borrels to constantly apply their effects
#3 Sheoldred March Of The Machine Market Price: $16.59 Sheoldred is a double-sided Phyrexian Praetor from March of the Machine
Mega Gengar ex SIR (Ascended Heroes, 2026): ~$1,200 The new-era grail
So until some FAQ on him is released I would say he is close to unplayable, you will be making up rules and spending insane amount of time trying to read the current rules to determine how his ability interact with them or reading conflicting intetperetations of how his ability works in given situations on both reddit, BBG and other places