If it's a qualified FI and it is a check out, I would log that as dual.
Depends what you're planning to use the time for though, will it actually be towards a licence application, or is it just general time in your book?
People get so worried about how or what to log, but you've only got to think about what it's actually for.
If it's for a revalidation, or an initial issue of a rating, you have to be pretty careful. If it's only going towards total time for either a future ATPL application, or for a potential employer to look at, I really wouldn't get that worried about it.