Don't we already have a man portable radar system? Not the newest of things, but still not too shabby.
On paper it might weigh twice as much, but that includes the whole kit. Including the terminal for display & control.
It also has the advantage of being a proper field tested bit of MIL-Spec equipment, Blighter on the other hand looks a bit fragile e.g. connectors that you'll snap off, and a not very robust tripod. And an MSTAR will work in extreme temperatures & conditions that would kill a 'rugged' laptop.
Then there's compatibility - standard equipment interfaces, and it runs on the standard radio batteries (or even a pack of AA's) rather than some unique to type lithium job.
I also believe the radar detection and target identification is rather effective too. Certainly you can identify someone just from them standing and breathing.
Not that Blighter is a bad bit of equipment. It's just that it looks like you get what you pay for, and it isn't a complete package or necessarily up to a full-on field deployment.
Probably OK as a network of 'cheap' sensors on a perimeter though, and given how things are in Afghanistan I guess that's how they'll be used rather than the way an MSTAR is usually deployed.