umh yes... so where is the Problem? Do you use more than 7 devices ? Keyboard, Mouse, Pen? Maybe a Smartphone so like 4 devices.
Using 3 at once (transfering a file from PC->smartphone, gaming = mouse+keyboard at heavy load) each using 5 Slots (625*5 = 3,125ms) so the input lag from they keayboard under heavy load could be 3*3.125ms = 9,375ms which is below the 16ms of a screen refresh and should not cause lag, should it?
The Bandwidth limitation is there, yes, but even for a Keyboard?
Logitech is also using their own 2.4ghz frequency with Multiple devices.
Found the Technical Whitepaper for Logitech 2.4ghz
http://www.logitech.com/images/pdf/emea_business/2.4ghz_white_paper.pdf
Says it's same as Bluetooth, bigger range, less energy drain, encryption, bandwith switching.....
Simply put "more premium features" than bluetooth.... but it does use a dongle ~.~