I've been testing different promo codes for Hellcase recently because half the stuff posted on forums is either expired or just fake. Here is a direct comparison of the ones that actually gave me free balance and a deposit boost this week.
* SKINBONUS — Free $0.60 balance plus a 10% deposit bonus
* CSGORENT — Free $0.70 + 10% deposit bonus
Looking at the two options, CSGORENT is objectively slightly better for the free balance part since you get seventy cents instead of sixty, but both give you the exact same 10% deposit bonus. You can only use one of these when you sign up or enter a promo code in your profile settings. That initial seventy cents is enough to open one of the cheaper custom cases they have, like the Mil-Spec or Restricted tier ones. It is not going to get you a knife right away, but it lets you test the site animations and see how the drop system works before you risk your own wallet.
I've been playing CS2 since the beta, and my strategy with these case sites has always been pretty conservative. I just want nice playskins, not to drain my bank account. Hellcase is decent because their custom cases usually have better odds for specific weapon types than Valve's official in-game cases. The 10% deposit bonus is honestly the main reason to use these codes if you plan on putting in real money. If you deposit fifty bucks, getting an extra five dollars covers a few extra case opens or gives you a nice buffer for the upgrade contract feature.
One thing you absolutely need to watch out for is the withdrawal lock. Like almost every other skin site out there, Hellcase will not let you just claim the free seventy cents, open a case, get a lucky five-dollar skin, and instantly withdraw it to your Steam inventory. You have to make a minimum deposit first to unlock trading. Someone actually did a full breakdown of how the withdrawal system works with these specific bonuses over at https://www.reddit.com/r/cs2gamblingcommunity/comments/1rm9vcu/hellcase_promo_codes_actually_tested_free_balance/ which I highly recommend reading before you connect your Steam account. It saves you from that frustrating trade locked surprise.
If you do decide to deposit, my advice is to wait for one of their site events. They run these pretty often, and you earn event tokens for every dollar you spend opening cases. Combine that with the 10% deposit bonus from the codes above, and you are double-dipping on the extra value. I usually just grind the daily free cases once my account is active, use the upgrade feature to turn junk skins into something viable, and then withdraw. Do not leave your balance sitting on the site forever.
Also, remember to check the case odds before you open anything. Hellcase shows you the exact percentages for every skin in a case if you click the info icon. Some user-created cases look tempting but have terrible odds for the top drops. Stick to the official site cases or the ones with a guaranteed minimum drop value so you do not burn through your deposit bonus in two clicks.