Not clear what it's supposed to cover. If you've got comprehensive insurance that should cover civil claims both for and against you arising from driving and you'll find that your insurer insists upon handling the litigation. That leaves criminal charges. When I did these for the RAC and trade unions, they were pretty poorly paid and therefore were work for the real babies of the profession; perhaps newly qualified pupils or tenants of a year's standing.
I never bother with it.
If someone has a claim against me, the insurers will sort it out.
If I have a claim against someone for "uninsured losses", there are plenty of "no win, no fee" lawyers out there.
I've used it twice. Once when a van pulled out in front of OH and crunched his car but the driver failed to co-operate. The legal people did lots of the leg work for us. And another time when it was not my fault and I claimed for uninsured losses. Its even more valuable if you are Third Party F&T
I wouldn't rely on "no win, no fee" because when you DO win they take huge percentages, and I mean, huge percentages of the claim in fees.
I've got fully comp and I don't need a courtesy car. I think I may err on the side of caution here though; £2 a month for more peace of mind and all that.