I've been watching the (hundreds of) Youtube vids regarding these Crown Crates and how many gems you get out of each to buy the items you do want with. It doesn't look good at all.
1st = you have to buy 4 crates and turn what they don't make you keep into gems to get enough gems to buy the cheapest item they have for sale; which is priced at 16 gems. (you get about 5 gems per crate if you sell back everything you can to them for gems)
2nd = the drop rate of high level items was so rare that one man bought 100 crates and didn't get a single mount; (but did get the cute black mask bear dog I want plus one memento) but another girl who didn't buy hers in one lump but over an 8 day stretch got one mount on day 7 (Senche Tiger) and another on day 8 (the Atronach Horse). Plus on day 8 she got the Senche Cub pet.
Both of them got numerous hairstyles and body/face markings for Khajiit & Argonian characters (though neither had them for any of their characters); both got numerous hats that made their characters look bald; both got numerous soul gems/potions/and speed/capacity/stamina points to spend at the stables. Both got numerous Crown stones.
The guy who bought all his in one lump got ONLY the same two costumes repeatedly and no others; but the girl who spread hers out over 8 days got several different costumes on different days (only one was adorable).
So it does
seem that buying one to a few crates a day may be a better strategy. (buy one, open it, if you don't get what you want buy another?) Like maybe by the 3rd crate if you are licked, realize you need to come back another day and stop buying them that day? Like maybe they are randomly filled with items by day, and the next day would be different items? I don't know.
I don't know if the results are random by when you buy them or when you open them; like maybe you could buy the 4 crate discounted price and then just open one per day? I don't know it depends on when Zenimax has the random set up; on open or on purchase.
Anytime a collectible item was repeated the player got gems instead of the item (because you can only have one in your collections due to them being by Player, not by character).
Example: cheap items like hats or body/face markings gave 3 gems; armor or costumes gave 5; and mounts or pets if repeated gave 33 gems.
From what the girl who bought over 8 days said, you can't just sell back the collectibles you don't want or can't use like all the Argonian hair styles - you are stuck with what you get on those and can only hope a repeat nets you gems.
Does not sound like a good investment to me, but I do see me getting hooked on opening unknown crates so will be staying away from them like I stay away from the "Unknown Armor" crates at the Merchants,