The cab pack is just his cabinets, but they're done incredibly well. I've tried a lot of add-on packs from a lot of different vendors and all of them had some artifacting or something else that made me not like them. Syn's cab pack is the only one I truly love.
That said, I was never going for "sound like Syn." I have my own tone and know what I like, which certainly has a lot of similarities to what Syn likes, but I've always just preferred to find my OWN happy place, tone-wise. For me, it was worth it, and I haven't found anyone who's bought them that didn't like and use them.