I'm not really a fan of splits because they usually just discourage me from further listening to the bands in question. I seriously miss coherence between songs that can be found on normal releases, and for the most of the time, they're just not long enough per band, and because of the aforementioned disappointment the whole release seems too long and dragging.
The two bands sound similar, with enough differences to make this ride interesting, as you'll see.
Insane Vesper: this is my first time with this band. The first name that came through my mind to describe their overall sound is some albums of Horna (Ordo Regnum Satanas), Satanic Warmaster (Revelation) and Ofermod (Mystérion Tés Anomias). It's good sounding (the guitar is perfectly audible) but still sports a raw edge. Vocals are those typical mid-range screams, mostly reminiscent of Mortuus. The songwriting is very good and faithful to this style, but it fails to bring anything brand new to the table (which is a good thing in my eyes, I mean, ears). The obscure atmosphere also reminds me of Cultes Des Ghoules, and even if they sound a bit differently, the songwriting was surely influenced by them.
Triumfall: you might have come across them if you're a fan of Gorgoroth, as they were signed by Infernus' label before Regain Records collapsed (taking the sub-label with it). As of the music, their material is rawer than the first half of this split, and they know what they're doing, pure Satanic BM. Here the drums take the leading role in the mix, instead of the guitars. The vocals sound uglier here, also more prominent in the mix, with a few clean chants making them more diverse. They actually remind me of some local (Hungarian) bands like Lepra and Witchcraft, even earlier Watain to some extent. The second track brings the (old) Watain influence a bit forward, emphasizing atmosphere with it, improving the overall experience.
Both bands show qualities that make them worth checking out. They deliver quality, just don't expect anything revolutionary on here, just the good ol' black metal you're already accustomed to. I'm not picking any winners here, because the differences themselves make both enjoyable on their own rights.