I found J & R on e-bay and thought the same when I needed a drive shaft for my 156 jtd last June with the same symptoms as yours - espcially as I'd expected very little change from £300 looking at other sources. What's more for the jtd the kit had short shaft, spider joint (the expensive and worn bit) AND a CV joint and guarantee for £60.
Took the plunge and gave them a call... OK, the guy I spoke to could have done with a few sessions at 'charm school', but me being from Yorkshire I could get his directness. The part was ordered 9am, arrived the next day and I fitted it the day after that. All problems cured!
Unfortunately, (yes the but), I cannot comment on the longevity compared to OEM parts asin Feb this year some (female) Volvo driver remoulded the boot of that 156 by running into it when I was stationary at lights and wrote it off. That said, If my current 156 needs the same, I have J&R's phone number in my phone.
Hope that says enough for you...