Anyone has personal expirience .
Are they practical, easy assemble on deck or in water?

I have no practical experience of them. Had a good look at one parked alongside of me a few years ago when a cruiser was passing through. The owner was raving about how good it was. In his case it was stowed on the foredeck when sailing and looked like an extension of the cabin. Quite clever how the join is set up. His was just rowed.

Swanson Snug:
www.seabreeze.com.au/forums/Sailing/General/Missing-link-the-Swanson-Pug-nesting-dinghy?page=1

I had a Swanson Snug for a while, had the sailing kit too but never tried it. Nice design idea. Not terribly easy to bring and stow both halves on board; the "stern" section will support your weight quite happily for dis- and reassembly but that's the piece you want on board first. The join is the weakest part, and needs to be beefed up else it cracks. The aft thwart isn't very comfortable to sit on owing to the necessary "V" section cutout. Overall a satisfactory tender without being a standout.

As per that link, this is the version I built. I made the transom very narrow, to fit the foredeck, as demonstrated by my young assistant:



Later it deserved some nice green paint and a sailing rig:


Above it had a locking plank as the middle seat, and there was a small seat near the rear, but not too far back:




This could be assembled in the water, because the cabin roof or foredeck was too small. 5 bolts and wing nuts held it together, but other dinghies use other means. My roto-moulded folding kayak from BCF uses a simpler 2 latch system, after the bottom clicks together.
My sailing rig was not fantastic, but in rowing or motoring the boat was excellent. It would take a few minutes to assemble, just like an inflatable but the skin is more rigid, so can bash or cut into waves much easier than an inflatable dinghy.