"on the flip side" is a correct and common phrase used in written English. It is usually used when introducing another point of view or when trying to contrast two ideas. For example: "Many have argued that the new policy will be beneficial, but on the flip side, it could have unintended consequences.".
On the flip side, boxers do have longer careers now.
On the flip side, the poor have typically slogged.
And on the flip side of that is the opposite.
On the flip side, we found it rather fetching.
On the flip side was a concerto by Prokofiev.
I put Hoochie Coochie Man on the flip side.
On the flip side, it's easy to test your work.
Ludwig does not simply clarify my doubts with English writing, it enlightens my writing with new possibilities
Simone Ivan Conte
Software Engineer at Adobe, UK