You're dismissing it too quickly. I've used this method on my stock contact forms and it has worked 100%. Nobody, nobody bothers writing custom bots for your thing, so, no matter which method you use, if it's not something common, it will stop 100% of spammers, if you're a low-profit site for them.
If you're Craigslist, sure, it won't work, but you probably aren't. All my clients' contact forms thank me for using (something like) this method.
If you're Craigslist, sure, it won't work, but you probably aren't. All my clients' contact forms thank me for using (something like) this method.