The modem supports tri-band operation for 3G and quad-band for EDGE and GPRS with a max support download speed of 7.2Mbps. We tested the modem on 3's network around East London using a Toshiba NB100 netbook. In terms of speed it put in a decent performance clocking up an average download speed of between 2.1 and 1.6Mbps with around 0.32Mbps for uploads.
Interestingly it produced these speed consistently rather than varying hugely according to signal strength as some other broadband modems that we've tested tend to do. In addition, the modem seemed to hold on to a signal better than some of its competitors, which may be a help if you live in an area where the signal strength for your chosen broadband carrier isn't the best.
Perhaps some of this performance can be explained by the Compass 885's use of Sierra Wireless' TRU-Diversity antenna system, which aims to improve performance in areas with lower signal strengths and reduce the number of dropped connections. As our results showed, it certainly seems to be having the desired effect.
On the downside the dongle does seems to draw quite a lot of power and we noticed that using it for prolonged periods on the NB100 seemed to reduce battery life by a about a third, which is something to bear in mind if you're planning on making heavy use of it on the road.
It's a tad disappointing that the 885 is a bit bulkier than other mobile broadband dongles and also that it places pretty high demands on your laptop's or notebook's battery. However, it's consistently good data rates and strong performance in weaker signal areas may make it a worthwhile purchase for some.