Free First 4MB of Each Data-Session Vodafone

Vodafone has recently changed the way they bill data on their Pay as You Go Plus prepaid plan. Minimum recharge amount is $10 and credit expires in a year (can be rolled over). This bargain is for people who have fairly LOW DATA USAGE, or people with usually low usage and occasionally high or very high usage (read further down).
Old billing: "2c per MB, charged per 512KB, first 512KB in each data session free"
New billing: "2c per MB, charged per 512KB, first 4MB in each data session free"
This is in all respects cheaper than the old way of billing.
I am still on a recharge from the old billing, and inside the vodafone app you can see each data session and the credit charge associated with it. It seems the app shows 1000KB of usage as "1.00MB", yet billing is actually "2c per 1024KB charged per 512KB". I must assume "4MB free" is really 4096KB free.
Data session?Determining when data sessions reset is a bit tricky, since every phone and every carrier is different, but generally it can happen after set periods of time, idle time, moving between towers, losing reception, turning mobile data off, switching to wifi, restarting/aeroplane mode. There is some speculation in this whirlpool thread.(forums.whirlpool.net.au)
From my understanding, throughout a day if you're connected to mobile data you will probably have a lot of sessions.
Gimme a scenario
Let's assume you use 100MB (100,000KB) a week, and you're the kind that generally uses it for instant messaging, and quick browsing sessions. To be super conservative, Sat and Sun will only have 1 data session each, and the weekdays will have 3 each, with data split evenly. Sat & Sun will be 8MB and 4MB usage, and the 5 weekdays will be 2 days of 14MB, 2 days of 18MB, and 1 day of 24MB. = 100MB over 7 days.