Hi - I am only speaking from personal experience on this one but there is no one method of getting rid of birds that works you will need to use several different techniques. If the birds are not protected then remove the nests and the eggs but make sure they are not protected first (your pest controller should be able to tell you this)
We have one of the airport shiny flashy things which is supposed to stop the birds from landing - it doesn't work 100% but it does help a bit (for £1000 you would hope it helped a lot more).
We also had a fake hawk - Doesn't work - they laugh at it after about 10 minutes.
We had a live hawk - really didn't work, was very expensive and upset the local residents - live hawking has to be done a lot, at the right time and will only work for certain birds if you can afford to have them come daily and the hawk is hungry and active I think it could work
The sound thing works but just like the flashy thing it isn't as effective as you want it to be and we found that after a while they got used to it (maybe we have deaf birds?)
Most effective thing I've found so far - block their nest sites, netting usually comes in to play which is expensive and make sure you get the right size. But blocking off holes and places where they want to nest is a good deterrent. Add on to that, giving them somewhere else to go, so we have a large site with some wooded areas and some derelict abandoned sheds at the edge of the site into these areas we have put nesting boxes and lots of food to draw them away from the factory they aren't causing a problem to the factory area and we plan to put a camera in one of the boxes and live feed it to the local primary school - we are lucky we have a big site
But even now with having all of the above I will still get the odd bird who wants to nest directly above the pedestrian access door and as ours are protected, once they have set up home there is nothing we can do until the winter and they fly off for their hols
If the pest company is selling you one method of dealing with them as the answer they are being a bit disingenuous, you need to use a variety of tools no one thing will completely solve the problem.