I have been pleased with the SSL front end on my Plus 8 for quite a while.
The 5L is a more serious investment that is certain, but in my opinion well worth while.
I tried a Plus 8 that was fitted with the Bilstein non-adjustable dampers and was very impressed with the ride quality, so decided to go ahead.
I am only 2 weeks after the conversion and have yet to find the optimum sweet spot for the dampers, but my initial comments are:
The first thing you notice has nothing to do with the ride, but the turn in is enormously improved. My Plus8 now handles like a sprightly 4/4, and I am really enjoying this extra agility while touring up in the Scottish Highlands. I have the adjustable Spax dampers fitted, and although I am still experimenting there an improvement in ride quality, but perhaps not as much as I had anticipated. I do however notice more difference when running with 2 up and full luggage and running solo. I think it is capable of delivering a really great ride once I find the sweet spot
The installation I looked at diy but was very glad I let Williams handle it under Peter Ballard’s specs on ride heights and suggested settings. It was quite tricky as the battery position had to be switched across the car and also the handbrake mechanism. Not jobs for those without some good workshop facilities.
So I do recommend it strongly but more for the handling than the ride.