I think the source of data is the same but it will be delivered in a more convenient way for you.So I take it the Nasdaq Total View subscription I have w/ IB is nowhere near that same named subscription direct from Nasdaq
I think one thing you need to keep in mind is that the value of direct feeds, and Level2 in general, is low latency. The more delay is added (by vendor or location), the less valuable/usable it is.
If you trade manually, there's a warning/confirm window pops up saying that you don't have market data. You will not be able to use hot keys. Also, you will not be able to to use Book Trader. If you trade via API, no data subscription is needed.I haven't try this before (ie without subscribing to IB data feed) but I believe you can still execute the trade.
Don't try getting better data feed prior to confirming that IB execution is satisfactory to your needs, imho.