TT Zega or BM Topbox?

Just got my 1150 GSA and am looking for a topbox, it already has Zega panniers. Should I go for a Zega or BM topbox. I want to lose the panniers when I go into London, so I need something to stash my lid and gloves in. Can the BM box hold a full face lid?

If its been covered before, sorry

Watch out for more stupid question as I get to know the bike better.

Brian

Do not know much about Zega, i have the BMW one and would not buy another one, they are too small, the rack underneath has broken and they attach ment to the back is dodgy.