TL;DR

Assuming you farm all the light tokens, you're not getting a free tank if you don't complete every single mission for at least 1300 tokens (on average).

FULL

I just did some math on the subject. Here are my assumptions:

• You can get roughly 41.85 tokens of light per gold spent
• You can get roughly 10.63 tokens of darkness per gold spent
• One day of premium is worth roughly 44.45 gold (when purchasing the yearly pack)
• One Swiss Franc (CHF) can buy you roughly 357.895 gold pieces (95CHF or regional equivalent for the largest 34000 gold pack)

Now, the light tokens can be easily farmed (it's just xp), so for simplicity's sake I'm assuming that if someone is serious about getting them, then (s)he will get them all, making them effectively free. The problem comes with the dark tokens, which are limited by the amount of missions that can be completed.

In total, to get one tank you need 112200 tokens, or 222400 for both.

For completing all missions for one tank, you receive 625000 credits, 2500 free xp and 6 days of premium worth roughly 2047.91 gold counting everything (800 credits per gold, 25 free xp per gold, 0.0225 days of premium per gold), or roughly 266.67 gold counting just the premium time.

For completing all missions for both tank, you receive 125000 credits, 49750 free xp and 12 days of premium worth ~4055 or ~533.33 gold respectively.

For comparison, current Sentinel bundle costs 20 CHF.

Assuming no tokens collected from missions, you'll have to pay:

• 10555 gold worth 29.49 CHF for one tank
• 20922 gold worth 58.46 CHF for both (29.23 CHF per tank)
• 10288 gold worth 28.75 CHF for one tank if you subtract the value of just premium time
• 20389 gold worth 56.97 CHF for both (28.48 CHF per tank) if you subtract the value of just premium time
• 8507 gold worth 23.77 CHF for one tank if you subtract the value of all mission perks
• 20922 gold worth 47.13 CHF for both (23.56 CHF per tank) if you subtract the value of all mission perks

Now, if you collect an average of 2000 tokens on every mission reset (twice a day), the numbers become the following, respectively:

• Gold / CHF / CHF per tank
• 5287 / 14.77
• 15654 / 43.74 / 21.87
• 5020 / 14.03
• 15120 / 42.25 / 21.12
• 3239 / 9.05
• 11599 / 32.41 / 16.20

Same case for an average of 3000 tokens on every mission reset:

• Gold / CHF / CHF per tank
• 2653 / 7.41
• 13020 / 36.38 / 18.19
• 2386 / 6.67
• 12486 / 34.89 / 17.44
• 605 / 1.69
• 8965 / 25.05 / 12.52

Too late to copy-paste another spreadsheet table to it, but a rough estimate: getting on average 100 tokens per reset more or less means paying 0.7 CHF more/less for both tanks.

SUBJECTIVE INTERPRETATION

I've taken premium account as a "bundle" option to the tanks, to make them seem a bit cheaper. As for free xp and credits, I wouldn't ever trade gold for either, but if you do, then here are the numbers.

Unless you can pull off 4000 tokens per reset from mission, you're going to pay at least a couple CHF for even a single tank., and expect to pay almost 30 for both even if you do.

Hope this helps someone.

EDITS

• typos
• table headers
• TL;DR