The trust oil sump increases the capacity and the sleeve around the new pickup acts as a baffle.
We put one on the Targa prepped GTR and had absolutely no oil surge issues.
The Jun one is just a baffle plate/windage tray and does not increase the sump capacity which is one of the biggest problems with the R. It is virtually the same as the Nismo one and all it did( yes, we tried that first ) was to delay the onset of the oil guage dropping.
My advice is if you are track running a GTR , have a very good fast reading oil pressure gauge with an adjustable red light.
I used that light to save my engine on a few occasions last year when I won the Enjo Speed Event Series.
Do the things Sydney Kid suggest but don't forget , they only have 4.5L std and with the std *oil up the top*problems, there may be as little as 2L left in the sump to run the bearings.
Cheers
Ken