Margaret
I have a BR20 with a stack pack system, my previous BR20 didn’t.
For my sailing just cruising with other half and dog I wouldn’t be without one.
Dropping and raising the main is very easy along with putting in a reef if required.
Against but manageable is you need to keep her into wind when handling the main as the lazy jacks will snag the battens, usually just the first (from the head) when raising. Also when shaking out a reef you will have to ease the reefing lines from within the pack as they tend not to run freely without intervention.
I originally had a topping lift as well, but this definitely increases the chances of a batten snag.
On my system the yard only installed two lazy jack lines down to the pack, this i found to be lacking in supporting the pack and keeping the opening open from front to back so I put in an extra block and made it into a three line system onto the pack.
One last thing, it would have been my preference to have the pack zip closure starting from the mast end, mine is from the clew, when dropping the main it is necessary on my boat to help the main down by pulling on the sail by the mast and and assisting the flaking into the pack, with the zip seating at the mast end you can then work your way back until the sail is tidy and well into the pack. Don’t get me wrong though, if single handed, put her into wind, release the halyard and the main will drop normally quite tidy into the pack certainly enough until you get her tied up.
As far as interfering with the sail when sailing it probably does to a minimum amount as the foot is always within the pack and as such will interfere with the air flow, but if you have a reef in on a non stack boat this I guess will be no different as the bunched sail will also have some impact on air flow.
In my opinion for my type of sailing with family, having the main kept nice and tidy when I’m finished for the day, it is certainly worth while.
One last point, the pack always has a small opening by the mast, tuck a piece of netting into it when not sailing as the birds, flies, love to get inside and make a nest.
Peter C