Ballard CatchPro bagger for ZTR

I have 3 medium sized oak trees in my yard. This was the first year that I thought that I was mulching too many of the leaves up and now want to start bagging them.

A full bagger system for my Gravely would run $1,500.

Ballard Products makes an aluminum catcher for $500. Reviews are great and I can move it from mower to mower, not just Gravely.

My question: the standard CatchPro is 4.1cuft. They make an extender that takes it to 7.0cuft. The extender does cost an extra $250. How much grass and leaves are we talking about with 4.1 vs 7.0cuft? I can buy just the 4.1 CatchPro then add the extension later, but if Ill need it right away, Ill order both.

CatchPro
Extension