To keep things simple and practical, why not just use the following (not sure if I got it right after reading thru Digi's site):

Principal: RM 80 (7GB + 3GB)
Supp: RM 38
Device: RM 10

In my case, I have 2 supp lines and need a device SIM for my tablet, it will work out to be RM 166/month for unlimited calls and SMS plus 7GB+3GB to be shared among all SIMs.

10GB (with 3GB on weekends) are already more than enough for my usage.
Not sure this plan I worked out is doable with Digi. If yes, I am tempted to MNP.

After re-read the notes, based on my example, still need to add RM 10 more (Internet Sharing Fee), making a total of RM 176.

Principal: RM 80 (7GB + 3GB)
Internet Share: RM 10
Supp1: RM 38
Supp2: RM 38
Device: RM 10
Total: RM 176 (Total 10GB)

Using Digi's example
Principal: RM 28 (0.5GB)
Internet Share: RM 10
Unlimited Calls: RM 10
Data 7GB: RM 35
Supp1: RM 38
Supp2: RM 38
Device SIM: RM 10
Total: RM 169 (Total 7.5GB)