Completely different products my friend....And there both very unique in their capabilities...A couple comparisons, based purely on my own personal experience and use. Both can be used in the sun, although Opt probably has a longer working time in the sun.
PB's cuts quicker (2.5 vs Opt) I would rate the Opt Polish somewhere between 2.0 and 2.5, probably closer to 2.0 though.
Opt can be worked for quite a while. This gives the user the option of additional cutting time. It doesnt ever seem like "it cuts, and your done". It willl polish until you have reached, hopefully, your expectations. It may be a little on the light side for actual "cutting" abilities. But thats easily resolved with either adding some compound, or switching to the compound altogether.
2.5 cuts immediately, it gets right to the task at hand, and accomplishes it very easy.
IMO, Opt can do what SSR's 1, 2, and 2.5 can do, but SSR's cant do what the Opt Polish can do. Analogy...
SSR's for immediate no nonsense polishing and cutting.....
Opt Polish for versatility.......
P.S. One of my normal routines is to use 2.5, and then clean up with Opt........