Also, I don't know how many exactly, but I think it takes more than a few chests to get a legendary.
This is mostly a gamble or depends on what exactly we are talking about. Sometimes there is no guaranteed artefact, for example when you buy the 3 chests of Marco Polo for 6 tokens each.
Sometimes the artefact is guaranteed after many chests and tons of money; for example, in the current offer for Leonidas' bust. There you buy 1 chest, then 2 chests, then 5 chests, then up to 10 times 8 chests. After that you get Leonidas "as a gift".
Since each chest has only 1% chance to get the artefact, the following applies
# purchase | # chests | total # chests | total chance to get artefact (at least once) |
1st | 1 | 1 | 1.00% |
2nd | 2 | 3 | 2.97% |
3rd | 5 | 8 | 7.73% |
4th | 8 | 16 | 14.85% |
5th | 8 | 24 | 21.43% |
6th | 8 | 32 | 27.50% |
7th | 8 | 40 | 33.10% |
8th | 8 | 48 | 38.27% |
9th | 8 | 56 | 43.04% |
10th | 8 | 64 | 47.44% |
11th | 8 | 72 | 51.50% |
12th | 8 | 80 | 55.25% |
13th | 8 | 88 | 58.71% |
free artefact | | | |
(The last 2 columns apply to
all chests with 1% chance)
That means after the 11th purchase you have just about a 50% chance of getting the artefact, but you already have paid over 180 euros (price/currency depends on your region!?).
Would you want to flip a coin for 180 euros?
The only "good" news is that you then get the artefact "for free" at 226 euros. (Sometimes the final price is even higher)