What pros and cons two-sided grill has if compare to pan?
The double-sided grills are pretty much a one-trick pony. Add food in the middle, close, wait, remove food again. Admittedly you can subject various foods to the treatment, but in the end, you get similar results, hot food with sear marks.

As soon as you want something slightly different, you are outside the thingy’s capacity. Just a few things you can do with a pan, but not with a panini / contact grill:


Stir-fry (meat or veggies quickly tossed around to flash-cook)
Deglazing (to use the searing residue in sauces)
Braising (adding liquid to finish cooking your dish in wet heat)
Frying/scrambling an egg (maybe possible if you can lay the grill flat and it has flat plates)
Cooking foods with different thicknesses and cooking times.
...


You probably get the idea. Now, I am not saying that a grill like the one in your question is useless. But remember that it’s the way more specialized tool in comparison to something as basic and versatile as a regular pan. If you are going to serve steak or grilled sandwiches on a very regular basis and if you don’t mind the cleanup (one word: grooves...), it may be an interesting investment. But I would guess that most cooks will rather reach for their trusty pan.