Does anyone have experience of Suplex springs?

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I am planning to rebush/generally refresh the front suspension of my Jaguar XJ40 soon. From looking online, it would seem that only Suplex is making new springs for the car. They seem very cheap - which has disconcerted me!

Has anyone fitted them to their car (doesn't have to be a Jaguar, of course) and if so, how did you find them?

My original springs are OK - not drooping as far as I know, but it seemed a good idea to replace them along with everything else.