The fact is that "Altitude Hold" is not lost when you are in Sport mode - the barometer is in fact still used when in Sport mode. The statement made previously in this post "The Sport mode disables barometer for altitude hold" is not true.
It is true that when running Solo at or near max speed, altitude can be lost - this can happen in any flight mode - even in Fly mode. This has been discussed a number of times already in this forum - with a stock Solo speed is not automatically slowed to allow altitude to be maintained.
The significant differences in this mode over Fly:Manual are that the Solo will fly faster and the Solo will hold the roll and pitch angles that you put it in even if you allow the stick to self-center. You must level the Solo yourself with stick movements. The autopilot does not regulate Solo’s roll and pitch angles so Solo will not automatically return to level. The roll and pitch angles are still limited, so even though it will reach steep angles it will not flip or roll (at least I haven't done it yet).
Some day I'll get the nerve to try Acro - I'll probably do it without gimbal or camera though.