With kit I ment the complete car. DEX410-R is a sort of budget-version of the DEX410, so some plastic parts instead of alu, and alu shocktowers instead of carbon. But the complete drivetrain, arms, hingepins, and all other parts are identical.
If your drivetrain needs replacement, you don't have many spares for your DEX yet and plan to race it regularly, buying an R version for spares is maybe a plan to consider.
Normal kit
http://www.team-durango.com/race-cars/dex410v3/
R-version
http://www.team-durango.com/race-cars/dex410rv3/