Top tube or frame bag a no no?

The one my mate had bulged out a fair bit and used to get in the way of the knees when climbing standing at times.
Though how much are you carrying with you if you're filling out a saddle bag and pockets?

My friend uses one and the fixing straps foul his back brake which makes it virtually useless. Other than that (and aesthetics) I cannot see a reason for not using one.
As far as drmatthewhardy's comment about pumps/tubes being kept in a jersey pocket, that, in my opinion, is a no-no.

Its the Rules:

"Rule #1 // Obey the Rules.

Rule #3 // Guide the uninitiated.

No matter how good you think your reason is to knowingly breach The Rules, it is never good enough.

Rule #31 // Spare tubes, multi-tools and repair kits should be stored in jersey pockets.

If absolutely necessary, in a converted bidon in a cage on bike."

I think the principle is, don't spoil your bike's beautiful lines.

I don't see the issue, apart from for fashion reasons tbh.

But then those are the same people who disapprove of saddle bags, frame-mounted pumps, non matching socks, non-slammed stems....

I expect that if they saw my top tube bag, designed for mounting on top of a top tube, and the realisation dawned that it is underslung under the seat frame on the front of a recumbent tandem tricycle, their hard-wired little fashionista heads would explode.

Fashion rules, for cycling? In the same era when retro-fashionistas brought about the re-launch of the Raleigh Chopper (or an object vaguely resembling a Chopper)?

Dog help us all

I think the appearance puts most people off. If you're happy with it, leave it be. It's your bike.