There is a vast range from stuff even sold by the likes of Aldi through to solutions like Automatrics.
A lot of the run of the mill ones, using 3/4G usually, will be defeated if someone is determined, while some of the higher end solutions which use a variety of methods tend to hold up fairly well.
Depends how much they are prepared to pay - the cheap stuff will probably do against your local low level criminal types but not so much if you have a desirable car which is likely to be stolen to order etc.
how old is the van? if newish maybe worth talking to insurance company they may have an approved system that can be fitted and save him money, to be honest if the van is that desirable they probably have suggested it.
if its just for the fact he carries tools etc in the back , the old answer i used to get from the insurance was remove them at night and lock them indoors, not always practical but thats insurance.
ive fitted one of the cheaper trackers into the daughters car (divorce and a dispute over who was going to get the vehicle, she got it at the end ,but he didnt give her the spare handset...) 6 months later i asked her how the tracker was going (runs with a sim card) and she hadnt even remembered to top up the card grrr