BiLateral Transit Agreements?

Does anyone have experience with BiLateral Transit Agreements, compared to the same with Peering Agreements? I have 2 ISP customers that are looking at such an agreement. While I can modify the standard BLPA templates to support transit provisions, I was curious if anyone had done so and what pitfalls to look for or considerations that should be made. Our particular case is high cost transport, so both companies are looking at each having a Tier 1 transit and then supporting the second through their agreement. Jack Bates