Just for fun, I decided to do a head to head comparison between Proraso Red and Cella Red. I used a Thiers Issard full hollow ground razor for three days and a Parker PTW Shavette with Wizmet blade for three days. I shaved one day with Proraso and one day with Cella with the straight razor, and then repeated with the shavette.
Scent: Oh man, that Cella smells amazing, even in the tub! I love that Marzipan smell. The Proraso is a sandalwood scented soap and in the tub has a strong chemical smell, to me. However, once lathered an on the face, that goes away and it has a nice, soft sandalwood scent that is not too sweet. I like it.
Lather: Both made great lather and were easy to get the consistency and sustainability that I wanted. I had peaks, but I wanted a moister yogurt, so I added a bit of water to my tips. To me, both felt great, but maybe the tallow based Cella felt a bit creamier. Both were nice, though, for the money.
Performance: I have found that for me and my environment, loading Proraso as I normally load other soaps is not optimal and performance suffers. I overloaded my brush enough to easily get six passes and I got far better performance out of the soap. The Cella, I overloaded just to keep things equal and I got good performance out of it, as well. I did three passes, WTG, ATG, XTG. With my straight razor, I had a bit of dragging with both, though I was able to do all of my passes, and even the scything XTG on my Adam's apple and along my jaws which are real problem areas. The shavette had no such issues. That thin, sharp blade cut through the whiskers with only a small amount of dragging. After all, these are not top tier soaps, but they are good enough to give a safe shave. I had enough residual slickness to touch up areas without re-lathering, though I found it more expedient to do so.
Value: Both of these soaps are inexpensive. There are some that perform better for me that cost less or slightly more. Still, for the money they are pretty good. The Cella cost me the equivalent of $9.40 USD and the Proraso cost the equivalent of $8.60 USD. However, I can get the top tier performing Shannon's Soaps Rebrab with the Chupacabra base for $9.99 and it is one of the best soaps I have ever used.
In summary, both of these are nice shaving soaps and not expensive. They smell good. However, for the same money I can get a top tier soap, so that is something to keep in mind.