Equipment comes and goes, it's a matter of fact if you stay in amateur astronomy for more than a couple of years. During the buying and selling, you might find that you could actually own a telescope or a certain piece of equipment more than once. I've a few such experiences.
1. Borg 45ED
Strictly speaking, I didn't own it twice, but I owned one Borg 45ED and one Borg 45ED II. They're very similar and the only difference is the focal length but you cannot tell from their appearance.
It's unique in the sense that it should be the smallest APO in the world. It's small and it's versatile. I used them mainly for solar imaging with my Solarmax 40, and it's useful for guiding and some real wide field scanning. High power observation is not useful due to the very limited aperture. It's so portable that you have no reason to keep it at home for whatever trip.
2. Celestron C5
This is a very unique telescope. It's an unique combination of size, weight, portability and performance and price! You cannot get any better than this given its portability. You can do some really "serious" work with the advanced video cameras these days, for example, my C5 Jupiter taken with a DBK exceeded my C8 Jupiter taken with a ToUCam Pro!
It's so light that any mount would do the job.
3. Various Cameras
I have owned more than five ToUCam Pro, some keeping their life as a color camera and some were modified to black and white. I sold them all until I bought some DMK/DBK.
I have owned three DMK/DBK, and they're really very nice cameras.
I have owned many Lumenera LU070M, they're perfect for their price, and I bought them as a batch from a closed research lab. They exceed the performance of a similar DMK with the higher dynamic range, bigger chip/pixel, etc.
