how to use the regularized rf in ranger

devtools::install_github("imbs-hl/ranger")
library(ranger)
data("mtcars")

regularized_rf <- ranger(mpg ~ ., 
                         data = mtcars, 
                         num.trees = 100, 
                         num.threads = 1, # needs to be set to 
                         # avoid parallelization
                         mtry = 7, 
                         regularization.factor = 0.3)

standard_rf <- ranger(mpg ~ ., 
                      num.trees = 100,
                      data = mtcars, 
                      mtry = 7)

# Prediction errors
regularized_rf$prediction.error
standard_rf$prediction.error

# Number of variables used
length(unique(unlist(regularized_rf$forest$split.varIDs)))
length(unique(unlist(standard_rf$forest$split.varIDs)))