I guess the big question is: Do you feel that you have upgraded from the Zeiss and Nikon to the Swaro.
A tough question, that. I think they're all on a par optically, with minor differences that don't make any one a clear "winner". If you like zooms, and prefer wide-field, that rules out the Nikon. If you like helical focussers, that rules out the Zeiss. Then you have to look at the ergonomics and which one suits
you best. Factor in the aftersales issue, and for me, the Swaro is my preference. That's not to say I wouldn't like a zoom eyepiece with a bit more mag than 50x (although I found the 25-50x more than adequate seawatching this autumn). So I wouldn't say the Swaro is an "upgrade" from the Nikon and Zeiss, but it has allowed me to "tweak" various issues and come up with the compromise I'm happiest with.
I should mention that any time I've lost eyecups, or the little plastic "aiming device" from the scope, etc., and needed a replacement, I've emailed Swarovski UK asking for a quote on the cost of a replacement. Invariably, the item arrives a few days later in the post with a "compliments" slip. They even cleaned and serviced a pair of EL's for me some years ago gratis, and similarly replaced a lens element on a scope eyepiece some time ago. I know it's easy to be cynical, but it's nice to know that as a customer, you're looked after long after you've made a major purchase, even though there is no immediate profit in it for the company. It makes you feel secure in the knowledge that with good service back-up, your kit will last a long time. And in the interests of fairness, I have had the same experience with Opticron, and Nikon sent me objective covers free (although the "service assessment" cost of getting Nikon kit actually
repaired by Nikon UK in Richmond is regrettable). By contrast, an email to Leica asking for the price of a replacement lanyard some time ago went ignored.