Diesel injector leak off test kits

[pcn1]

https://www.ebay.co.uk/itm/266583536267?_skw=engin...

Are these kits ok, just they seem very cheap?
I'm trying to track down a slightly lumpy idle problem on the 5 cylinder Mercedes 2.7crd engine in my Jeep.

Also, any hints or tips to get the best out of them ?

[Novexx]

Yes, fine - manufacturer approved leak-off kits look about the same, some worse.