After living for quite some time with the wi-fi built into the ADSL modems (I have two lines at  home) I’ve decided that the signal needed some improvement to work reliably with the Nexus 7.
For this reason, after reading a lot of reviews online I’ve selected this small device: it’s not the cheapest device for the purpose but I trust Smallnetbuilder

The design is unconventional and the size was surprisingly small when I got it.
The installation manual is relatively fat but it’s only because it covers a dozen different languages: the actual content is quite skinny; this fortunately is not an issue as the setup, once connected to the web interface, is really easy to do.

Signal improved significantly on the Nexus 7: from 1-2 tabs with some occasional complete disconnection to 4 bars (out of 4) with few drops to 3 bars.
Also the Nokia Lumia 800 and E7 both have shown a significant improvement in signal quality.
The Acer 3810T was already working fine with the older solution: this is likely due to the larger radio antenna and greater available power.

The device can be used also as a wi-fi to ethernet bridge to connect a single device implementing in an easy way what I did using OpenWRT and to extend the wi-fi range, but I’ve not used it in this way.

Overall I had a very positive experience and would suggest this device to anyone having a need like mine.