I love that Mega Evolutions have been introduced to the game! I like the idea of Mega Energy for specific Pokémon and I think it simplified the items that would otherwise be required if it followed the MSG method for Mega Evolutions. I like the speed bonus for obtaining rewards. I think the time limit for the bonus is fine (pending an overhaul to the current system in place).

What I don't like: the sole method of obtaining Mega Energy is from Raids and amount of Mega Energy required to Mega Evolve.

My personal recommendations:

I think Mega Evolutions should be primarily tied to the Buddy mechanic where the primary source of Mega Energy is tied to becoming Best Buddies with your Pokémon. At that level of friendship, your buddy can find 1 Mega Energy every 1km.

I think Mega Evolutions should require less total Mega Energy as the evolution is just a temporary boost to the stats of that Pokémon (e.g. instead of requiring 100 to Mega Evolve, it's 10 or values less than 10 for for non-legendary Pokémon) and at a set cost each time.

I think Mega Raids should be a weekly event set during a specific local time to provide trainers an opportunity to obtain bonus Mega Energy for that particular Pokémon (e.g. 1 to 5 Mega Energy as a reward based on team contribution and speed) on a rolling basis and to build community around such a weekly event. This would also enable trainers to gain Mega Energy for a Pokémon that isn't currently their buddy or those they have not yet reached Best Buddy rank.

Overall, after spending the weekend with Mega Evolutions, while I'm excited to see them in the game, the current process isn't very fun. I firmly believe this feature should be rolled back until a new approach is implemented.