I finally had the chance to plug it in briefly tonight and... Wow! Fantastic tone. Definitely far brighter and growlier than the current Gibson Thunderbird pickup - in fact it sounds just like an old classic Thunderbird. For those going after that Martin Turner tone, the neck pickup nails it.
To my ears, the tone with both pickups blended is slightly tighter that the classics but that's to be expected as the bridge pickup is closer to the bridge that it used to be. The neck pickup though, it just roars. Filthy beast!
I think my initial impressions were a bit harsh - probably because it's a brand new, shiny thing that has never been played, I rarely buy brand new and I'm use to things being a bit more worn in. I've just spent a very pleasurable half hour finding my way around it. Amazingly, no neck dive either! It does hang in a slightly odd position compared to what I'm used to, but again, that's just the nature of Thunderbirds.
I'm not 100% if it's staying yet, but it's rapidly growing on me.