done my 10K servicing (at every ~4mths) at Autosaver with free N2 top-up.
when topping N2, pls ensure proper procedure;
1. set to desire pressure and plug-in nozzle
2. N2 will start to inflate to "desire pressure" first (*therefore Compressed-air + N2 in tyre)
3. on beeping "END" shows, then it will start to completely deflate tyre (*remove All air, tyre become soft)
4. after this, N2 will start to inflate to your "desire pressure"
*for above procedure, each tyre will take ~5mins to fill N2 completely.
*very often, some shops only do step 1~3 (*unethical !!)