use of SPF include for secondary MX

[johnc]

I'm planning to use rollernet servers as my backup MX server. For this you advise using an spf include in my spf record (include:spf.rollernet.us). In the course of reviewing my spf records with the advisors at openspf.org, I am told that I should not use this include, but that I should exempt rollernet origined mail from spf check by my main server. Could you clarify best practice here?

[RollerNetSupport]

Messages from our servers should be generally exempt from any kind of further filtering - especially anything that may cause a bounce - but we still provide alternatives for people who can't fully whitelist our servers. We recommend using whatever works best for you.