Really depends on where you plan to cycle.

Personally I wouldn't cycle in Buenos Aires without knowing where I was going as it is not very cyclist friendly from what I have seen. At least the OP has the sense to go with an outfit who will know the quieter routes.

Out of the capital the main trunk roads are a nightmare to cycle on and so when I go out of my town I just stick to the dirt roads although you then have the problems of dust if they are dry or mud if they are wet.

If you stay off the main routes especially the ones the lorries use cycling is safe and a great way to see the countryside. We drove from Neuquen over to the St Martin de Los Andes area on a paved road and there was hardly any traffic at all. I made a mental note to get down there some time with the bike in the future and do a tour. I am sure there are many more examples