Now, any major firm that works with startups will defer costs until a raise or early exit (save the incorporation costs to the state).
Now, you'll always have tradeoffs. A personal relationship with an attorney, even if it's a friend of a friend, gives you better access and stretches the amount they are willing to help, especially when it comes to advice or referrals. However, if you don't have an in with the attorney, you'll have to cultivate that relationship like you would with any other contact.
Now, do you interview the attorney? Absolutely! And make sure you interview both the partner and the associate, if you choose a larger firm.
The most important criteria is trust. You can't expect the attorney to spend countless hours customizing docs for an unknown startup, that has yet to warrant the labor, nor will likely have the ability to pay (after all, if you don't raise / exit, they write-off the costs). However, good advice, availability and willingness to make an intro (if they think it's germane) is important...so talk to other clients in your situation.
No regrets.