2MX records with each 2 IPs - valid by RFC?

Hi,

we have two ISP connections with separate ip ranges.
The MX records have the same prio and point to 2 Spamfilters.
From my understanding it should be enough to have a
config like this:

mx1.domain.com -> 100.100.100.1 (Spamfilter 1)
mx2.domain.com -> 200.200.200.1 (Spamfilter 2)

But somebody wanted to change that to this:

mx1.domain.com -> 100.100.100.1 (Spamfilter 1)
mx1.domain.com -> 200.200.200.1 (Spamfilter 1)

mx2.domain.com -> 100.100.100.2 (Spamfilter 2)
mx2.domain.com -> 200.200.200.2 (Spamfilter 2)

Is this config valid by RFC?
What is the benefit of the second config?

Thanks!