You know what most people don't realize? Just how versatile this card is. Yes, speed decks can use them, and yes, speed decks will mostly appreciate it. But I'm just going to name a few Pokemon that will also love this card, see if you can figure out why I name them.
Butterfree GE-Expert Belt ups this guys healing attack, and 140 HP is nice on a free retreater
Bastiodon PT-He heals in between turns, and with special metals he can tank effectively
Cradily LA-He can do his finishing KO on a 50 HP or less benched pokemon, which means less damage for his uber healing to work.
Shuppet PT-Fade Out will do more damage, and there is no real drawback as he goes back to the hand with his belt (well maybe gengar)
Uxie LA-Same thing as shuppet basically, but he can avoid fainting spells from gengars with less damage, and can get more damage off and escape to the deck
Mismagius GL LV.X RR-Picks up expert belts from weak pokemon.
Porygon-Z Promo-This is a hard one. Gives it more HP and damage to achieve higher damage even with 8 TM's perhaps?
Nidoqueen RR-Expert Belt can help this thing to get the magic 130 mark when the opponent has a full bench. Queen also helps tanks with expert belt attached to them by healing in between turns.
Just a few cards that will appreciate this, some for more obvious reasons then others.