I've owned the SM450 & also BP10B around the same time.
I think bipole/dipole speakers will have an advantage over direct-radiating/monopole speakers in terms of overall spaciousness and 3-dimensional imaging. This translates to a more life-like natural sound IMO.
But if I were to compare the SM450 against any other direct-radiating/monopole speakers out there, the SM450 will hold it's own extremely well IMO.
The SM450s' tweeters are as smooth as any speakers I've heard IMO.
The SM450s' midrange are as clear as any speakers I've heard IMO.
I think the bass response is about 60Hz @ -3dB below 90dB from 1 meter.
Regarding the Audio Critic's review in which they compared the small SM450s to the much bigger B&W 800 Matrix towers, the SM450s held their own in terms of midrange & high-frequency performance. The ONLY area the SM450s trailed the B&W 800 was the bass.
If that is not a huge endorsement, I don't know what is.
The one thing about bipole speakers is that you need some space to achieve maximum performance.
I don't have issues with space, so I would always prefer dipole/bipole speakers over monopole speakers.
But I think the SM450s are great sounding monople bookshelf speakers when compared to any bookshelf speakers out there I've ever heard, including the $2,000 Revel M22.
I think the BP10B sounded great. However, I have never auditioned the BP6B.