So "bag deposit box" was on sales this weekend and I bought 2 (250 slots each) of them to bring up my total bag deposit slot to 520.
I put my 2 large collectible bags (80 slots each with 1 full and 1 at 40 slots full) in the deposit box and behold, total of 410 slots were taken up!
So 120 slots that was taken up in my collectible bags took up 390 slots in bag deposit box.
Turns out that while the collectible bags can stack up to 1000, bag deposit box only stack the collectibles up to 100.
So if I had 955 small eberron shards, it would only take 1 slot in bag but 10 slots in bag deposit box.
Had I known this, I would of just bought a bigger bag instead (cheaper than about 1300tp i just spent).
Also, I should mention that paging through the bag deposit box (over 10 pages now) is painfully slow. If you don't know exactly what you are searching for (you can search with text string), its a slow slow process to go through the inventory (no sort option either).
If bag deposit box is working as intended, I think it's very poorly implemented.
If you want to dump items in the bag that you don't have lots of quantities of then perhaps it's worth it (as long as you can remember what it's called) but for dumping everything that was in the bag like I wanted to do, it's just more hassle and uneconomical.