First the industry standard for contract negotiation is to determine if you even need a contract like this that has to be "signed" and/or negotiated.
Missing is the dollar amount of a transaction or type of transaction that using an agreement like this relates to. It's overkill for many transactions and will kill deals. Companies don't sue over small amounts of money however deals do get killed if you give customers to much to think about.
Specifically:
"We've just open-sourced a sales agreement any company can use. Though obviously you should use this at your own risk, we've had a lot of experience with what makes good and bad sales agreements."
If you leave it up to the lawyers they are going to try and wrap up every single detail without considering any of the downside risk to having a customer have to review an agreement. Many of these agreements came to being by corner cases of liability that are few and far between.
Bottom line: Make sure to consider if this is necessary in this form at all (for your company) and if there is another easier friction (edit "free") way to provide some protection. This is not a case of "it can't hurt" it can hurt getting a sale.