I have 3 different types of sat nav.
Via Michelin, Tom Tom and Navman - they all do that.
To get through that many drops - most I ever did was 62 plus 4 collections in an area I knew, you will have to have some local knowledge. By the time you have entered all of them in you will have lost any advantage that the Sat Nav gives. To put 50 in would take around an hour. You may find that there is a limit to how many drops you can put in at once.
What the Sat Nav will not do is give the best route and more importantly drop order. You will have to sort the drop order out yourself and usually you do that while you load the van to make sure you can easily get to the things you need in the right order. To sort out a good drop order and so the best route you will have to use a map sometimes anyway.
Sounds like you have just secured a job for the run up to Xmas for one of the parcel carriers. Been there, done that, will never do it again. I love driving but that is the worse job I ever did.
If everything goes well it is still a pig of a job. Just one duff address can ruin the whole day - and you get some that sat navs or maps are little help for.
Good Luck - you will need it.