The airlocs have to be terminated using specialist equipment (at your dealer). I have used QED screwlocs which are great but they cost about £14 for 4.
The purpose of a plug is for convenient and robust connection to your speakers/equipment. It is probably better than hardwiring because you can get a good connection (providing you screw the cable down tightly) and there is less of the actual wire exposed to the air.
Depending on the quality of your speakers, cable etc. I would suggest that £1.50 ones should be OK but if your equipment and cable is expensive and warrants it, go for the screwlock. IMO there is no need to go to airlocs.
At the end of the day all you are after is a good sound connection however it is achieved.