The springs on your vehicle are calibrated specifically for it, based on the number and weight of extras installed during its manufacture.
Numerous forum entries indicate that owners who have installed aftermarket springs often find their vehicles either too elevated or insufficiently lowered compared to the appropriate stance with OEM components.
In response to your inquiry, they are indeed a respected company; nevertheless, for a little additional cost, I would recommend acquiring the appropriate components, particularly if you want to retain the vehicle.
Have you inquired about a discount from the dealer? - Consider contacting MB Grangemouth, since it may be worthwhile.