Personally, I find some of the Rihannsu material to chime more naturally with the Romulans as they are portrayed in the Star Fleet Universe, then perhaps with those seen in the TNG-era Franchise.
With no Nemesis-esque Remans (or Remus, for that matter), no brow ridges in sight, and a strong focus on the concept of honour, the echoes ring more clearly - the SFU Romulans even call themselves Rihansu (one n), though the term has a somewhat different in-universe meaning (deriving from the old term Kiay Ri-ha-nai, or 'unifying duty', which had competed with Kya-yai, 'Logic', in the time of Surak).
Although, one thing which really stood out for me was how crappy the Romulan and Klingon ships were, compared to those of the Federation.
(I prefer to have a closer degree of balance between the upgraded Romulan hulls and the converted Klingon ones - what the SFU would call the Eagle- and Kestrel-series - and the ships of Star Fleet.)
But then, there are more than a few books which are less than fairly balanced in that regard, so I try not to take too much mind of it.
I don't see too much of a problem with considering this series of books as in a separate/splinter timeline to other Franchise novels or series - they are equally non-canonical compared to TV Trek, but can find equally valid (and non-conflicting) places when treated as part of a range of, to note a previously-coined term, myriad universes.
It's a big enough multiverse to go around...