I think, you might be needing a lot of funds when investing on gambling site because they have minimum funds to be accepted and its kind a risky move because its all or nothing and win or lose situation. However , gambling is not an investment but a game where money counts and not just a number.
The minimum amount required to invest in gambling site's bankroll is 0.01 BTC(some require even less) and it's not that risky, over long-run you will make profit. the more you'll invest the bigger returns you're going to get.
How can any investment do not even have a risk to take? Moreover it is much depends on your kelly if you said about risky thing. If you place on 10x kelly, you will gain profit in no time but sure you need some bankroll to sustain some big win there. But if you only play for around 2-3 kelly then 0.01 btc of course will be enough to get some profit