Well, I handle it like this:
I buy premium account for extra arena coins.
So I only “need” it for those 5 battles a day and not nonstop for 24 hours.
As such I “only” buy those 8 hours of premium account each day.
So let’s do the math:
today 16 tokens + tomorrow 16 tokens (thanks to sale) + 22 tokens * 28 for the following 28 days without sale = 648 tokens for 30 days.
= 21.6 tokens a day
Compared to that the “best value” per day from the sale:
30 days nonstop premium account for 937 tokens
= 31.23 tokens a day
So it is far more expensive than just buying those 8 hours every day even without that discount.
Btw. if you have the opportunity you could play like within 4 hours before the daily quests reset and within 4 hours after the reset of daily quests.
Even within just 1-2 hours before the reset and within 6 hours afterwards or vice versa within 6 hours before and 2 hours afterwards is also possible.
Then you can buy 8 hours premium account and do those 5 battles before the reset and then after the reset of daily quests within those 8 hours.
That way you could even drive down the costs to:
16 tokens altogether for 10 PvP battles of today and tomorrow + 22 tokens * 14 for the remaining 28 days paired into half before the reset and half after the reset of daily quests.
So then the total is only:
16 tokens + 22 tokens * 14 = 324 tokens for 30 days.
= 10.8 tokens per day
Hence if you only want that premium account for additional arena coins then that sale is not really worth it as the 8-hours-premium-accounts would only cost you 1/3 to 2/3 of the “best price” per day of this sale.