I faced the same issue nearly 20 years ago when I got my 550B. However, I already had dies in 38/357 and 45 Colt. I use RCBS Carbide dies. I simply bought caliber conversion kits with the powder funnel and loaded on the 550 with the RCBS dies(I did buy a 3 pack of toolheads and powder dies so I didn't have to readjust those). I swapped the powder measure each time I changed calibers and adjusted it (until I bought more of them). Later, since I was loading lead bullets, I bought Dillon's seating die which has a nice drop out insert to clean the lube/gunk out, and gave me separate seat/crimp stations. Buying RCBS dies and Dillon's seat die was still cheaper than only Dillon's dies. I would still do this today, however I do agree the Dillon size dies have a nice radius at the bottom that ease's entry into the die, but if you adjust the shellplate properly, it's not an issue. I have one set of Dillon dies, in 223.
That all being said, I doubt those RCBS dies have ever ventured out of the 550B toolhead, except the seat/crimp which was moved to crimp only after I got the Dillon seater. So I never went back to manual loading for those calibers, ever. The expander sits all lonely in it's RCBS die box.
If you get into some really odd calibers, Dillon doesn't make die sets, but you can use other brands, and Dillon will try and help you find the right shellplate/funnel combination to load on their machines. Most of the time if can be figured out. Particularly for the 550B, which has a lot of versatility.
If it were me, I'd set the calibers up for the Dillon. And if I had the money, I'd buy it all at once to save on the shipping. I didn't so I piecemealed over the years like most of us do. However, since 45 Colt is fairly expensive, and fairly cheap to load (and the factory offerings were terrible 20 years ago), the cost savings repaid very quickly.
Like the noylj said, it's what you want to do.