Sealed Vault is a silver bullet that shuts down Account Siphon (and Vamp). However, most players turn to the more flexible Crisium Grid that not only stops Account Siphon but can also deal with Keyhole. Having an extra economy card instead to help you recover from/mitigate Account Siphon isn't a bad shout either.

However, Sealed Vault's surprise factor should not be overlooked. A surprise rez means the runner still takes two tags they might not be able to clear. More importantly, it disrupts their plans and prevents them from capitalizing on the Account Siphon in a way that simply running more economy wouldn't.

It goes without saying that this card is best in decks that are particularly vulnerable to Account Siphon. Rich corps or those with a well/decently defended HQ should bypass it. Overall, its application is too niche to see a lot of play, but when it fires, it really hurts.

Don't forget a runner can opt for a normal access with account siphon, so they are not likely to take two tags with account siphon if you've sealed your credits away. —
not if they used eater ;) —
Letsaros: no, they can still "proceed to the access step" if they used Eater, then access 0 cards and take no tags. —