For sure you can win big, my biggest wins were on stake originals. But you can also lose very quickly, and if your addicted to gambling (like don't know when to stop) you could be like the half the people who play them and drain your bank quickly chasing wins
I think they send them out when you wager a bigger amount (usually 10% + on the vip progress scale), in a 24 hour period. I've gotten a few of those emails, but only after I've wagered atleast 100k in 24 hours😜
*I could be wrong, this is just my experience!