Of course a Kifaru Guide Lid would make an excellent gift!
But.....it's a Tough call brother. Depends on their "day pack" usage.
I pulled my guide lid off the pack and used it to carry bladders down to the creek for refilling. Had 2 100oz bladders, a nalgene, and a 16oz bottle crammed in there. Didn't fit great but enough that I didn't have to carry all 4 individually or have to take my whole pack down for a water run. That said...the weight of it would suck riding on my back all day like that. It worked but not super comfortable and wouldn't want to run around like that all day.
I've pulled it off and used it as a quick scouting pack with a jacket, possibles pouch, nalgene, etc (very small light load) and it worked perfectly. It's a great "grab and go" item.
My son has also worn it around town (park, zoo, museum, etc) when we travel and it works great for a smallish load. (I run an urban zippy and he wanted to carry a Kifaru "day pack").
So....with those examples of my usage I would say it's a great super light weight day pack for light load when you know you're not gonna need to carry heavy items all day long. But once you start creeping up in weight you might want to think about a different style day pack.
Hope that helps.