Probably not as an average sized bloke, they do however have weird sizings.....there is a thread [here] which relates to measuring the circumference of your wrist, and Microsofts official wrist sizing guide for the band 1 to print out [here] - ensure you click on the link for band 1 not band 2! . Really you need to ascertain both I found, and even then until you try one on you can never be too sure.

For myself I took a piece of string to measure and my fairly average wrist circumference is 18.8cm

According to the link for jojo42 guide the following applies

Medium band: wrist size of 7" (about 18cm) gets me to the middle of the adjustment range. Perfect fit.
Small band: wrist size of 7" / 18cm just barely fit on the widest band setting.
Large band: wrist size of 7" / 18cm leaves the band a bit loose even on the tightest setting.

The adjustment track is about 1" long, so that means roughly

Wrist sizes between 5.75" and 6.75" get a small (14.5 - 17cm)
Wrist sizes between 6.5" and 7.5" get medium (16.5 - 19cm)
Wrist sizes between 7.5" and 8.5" get large (19 - 21.6 cm)

As can be seen from that I am at the upper end of the medium and the tightest setting of large would leave it loose, as I loose weight (one of the intentions of buying a fitness tracker for me) my wrist size will thin in circumference....however.....

This is not exact science because it depends also very importantly on wrist height. there are three sizes as per the Microsoft guide, measure your wrist with that...I fit literally just inside the medium bracket, and with my wrist circumference according to jojo42 I do find as suspected a medium fits me with only slight adjustment. If I had gone for large I am pretty sure tightened right up not only would it have been too large for my wrist circumference but also way too much for the height of my wrist.

The heights are as follows :

39mm Small
41mm Medium
49mm Large

It is a crazy jump between Medium to Large regarding wrist height, and clearly for me Large would never have fit right even though I am literally at the upper end of Medium with very little on the adjustment slider (sometimes I found it a little uncomfortable with temperature changes and need to slacken it off to near enough maximum circumference adjustment.

Hope this helps.

Awesome deal, just picked mine up!

see this post of how to get for free http://www.hotukdeals.com/misc/get-o2-priority-moments-free-even-your-with-o2-1780561

Great deal, I'll pick one up soonish

thanks just got one for him indoors!!

Dammit! Wanted to get one of these as a present when they were £50. Ended up getting a Fitbit at £65. Now face a decision of whether to return it.

If its microsoft does it take an age to start working and then gets more and more bunged up and eventually grinds to a halt?

Which band version is this?

Just note this is the older version and has been superseded. That said, it is still a good deal.

More information here: http://www.anandtech.com/show/9821/the-microsoft-band-2-review including a table comparing the two devices.