Actually special round is done after all the 7 rounds of jossa completed and there are very rare chance of getting admission in these rounds if you are having rank of under 25k in general and 15k in OBC then there are few chances of getting NIT in spot round round.
Not sure about which branch you are going to get there might be chances that you get lower branches in lower NITs and few IIITs and it is what always this happen is that the branch allotted, institute allotted in spot round is not accepted by the student.
So I will suggest you never take a risk of special round.
By doing this you may not able to fill the registration forms of many other colleges whose last date is always before the June end.
One of my My friend who get NIT Srinagar in spot round he goes there and studied for 2 months there and unable to survive there and he left the BTech over there and start preparing for JEE mains once again and this time he was able to secure good rank and get admission into a good NIT.
Many other my friend allotted institute of North East NIT even out of them few came back after 2-3 months and start preparing for JEE mains ,