It’s a good quality but sugary mix .
I dont feed sugary mixes unless I really need to tempt a horse to eat and have failed to get other things to work .
Ive been feeding happy hood chaff, and just some supplements with a bit of veteran vitality. His old owner used to use pasture mix with him and he seemed to go ready well with her.
Why? Its a serious question. What are you trying to achieve? The spring grass will be coming through soon if its not here already. I would weigh tape, condition score and then decide if you need to give extra calories, if you do start with extra forage. The next step is a low starch/sugar feed. https://www.bluecross.org.uk/fat-horse-slim this has a link to a pdf about condition scoring.
He just seems to lack the energy. Just something to sprite him up a bit. I just thought as his old owner used to use it and I heard it added a fair amount of energy and gave horses the sparkle they lacked. I ride 4 times a week doing a bit of everything so anything he puts on will be worked off.