Others can answer on their own experience, but here is something to think about from the AFE website (numbers are for the 4.4, they don't have a graph for the 4.8). This is what they use to sell this product:

Stage 1 (Magnum) replaces the stock airbox.
+10 hp at 3200 rpm
- 30 hp at 2200 rpm (that isn't in the headline, just reading from their own graph)
More torque at 2000 rpm, dropping off quickly and not recovering to stock torque levels until 2700 rpm

All this depends on whether you trust their graphs as well. I think the appropriate term is 'sample of one' with some questions on the repeatability of the test data.

Without digging into it, I would put the Dinan intake in the same category.

So, which is best? Whichever one looks best to you, since overall it is nothing more than a cosmetic upgrade in any case. Others can comment on price, appearance, and reliability of the vendors much better than I can.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue