Lovely through neck bass,I reckon made in Indonesia but much like the Vietnamese Grind BXP.
No idea about the passive Cirrus though I've saw it on an ebay seller's spiel. Cirrus have a wide cut to the lower horn,Zephyrs don't.
Cirrus have VFLs,Zephyrs don't. Cirrus have ABM bridges,Zephyrs don't.Cirrus have graphite, Zephyrs don't.Cirrus are 35" scale,Zephyrs are 34" scale.
You see a pattern forming
That said what is the Zephyr like ? Same flat top humbucker pickups as the Grinds, 2 volume 2 Tone, High mass bridge. Neck is slightly thicker front to back than on the Grind,I'd also say the fretboard radius was different. If I can lay my hands on my gauges I'll tell you what the radius is.
My Zephyr 5 had knackered pots so as I was changing them I added a preamp. I swapped the pickups too,not that they were bad just I was souping it up so might as well stick in new pickups.. I've heard from some folks that they expected more from the pickups but that's down to personal taste/string & set up.A recent owner of a Vietnamese Grind told me they prefer the Zephyr tone but feel of the Grind.
I'll admit to being a fan of the passive Grind so think highly of the Zephyr but the Zephyr is far closer to the Grind than the Cirrus. Couple of year back they were selling for £100 but a really nice 5'er sold few months back for £200.I had a few bids on that 5'er myself
Upshot. Well built,great playing/looking bass with the jury out on tone.
When I go looking for the gauges I'll try and dig my BXP Cirrus out,could be that's the Cirrus they mean and not the USA Cirrus