The Ebay link and the Maxmarineshop link are actually one and the same vendor.
The partnumber seems to match the partnumber referred to in the installation manual of B&G, assuming Amel used the straight version. They came in the original B&G box carrying that number.
I have not examined the way the are mounted in detail as mine are still working. But they must be mounted from the underside I would say. There is a tube inside the hull leading all the way into the bilge.
I’m guessing the sensor is pushed in the hole bedded in Sikaflex. So I’m sure it will be a pig to remove once the time comes. I guess the best way is by drilling a hole in the face of the sensor and putting in a large screw to get some leverage to pull it out. Remember to tie a piece of string to the other end to feed in the new sensor once the old one is out.