Here's my experience with the 301:
I remember the day the Bose rep came around and explained there was a new speaker in the line - this would have been about 1977 or so - to compliment the 901 and the 501s. It was to be an 'entry' level speaker to help dealers sell more Bose speakers and take advantage of upgrades.
The Bose rep arranged for us to come to a local hotel where he had rented a conference room for the unveiling and demo. Earlier in the day he had come to the store to borrow some gear; he took: Pioneer SX-1010 receiver, a Sony PS-X6 turntable and a set of JBL L-100s to complement the Crown tape recorder he brought. The sales guys on the floor snickered that this 'evening with Bose' was going to be a debacle - "what on earth would these 'entry' level speakers do with a set up like that?", they asked.
So, the store closed and we all went to dinner on Bose in the conference room where the gear was all covered so we couldn't see what speakers were being played at low volume throughout the dinner. The gear was arrayed along the long wall of the room and our seating put us right into the point of what we now know as the Cardas triangle - the sweet spot.
After dinner, the rep then went into what was clearly a presentation he had done many times (thank goodness we didn't have PowerPoint back then!). The demo itself consisted of a well-recorded tape of both live recordings and some well-known recordings typically used for demos in that day - Sheffield Labs, etc. Of course, the speakers were switched back and forth quite a few times and at various volume levels including _very_ loud. We were not allowed to see which ones we were hearing and any given time. At the end of the demo, the rep asked each of us to determine what speaker we had been hearing - a blind test sort of thing.
Frankly, I had great difficulty determining whether I was hearing the JBLs or the 301s. There was no trickery in the demo - just the use of the Pioneer's A/B speaker switch. The only real difference I could hear was the the JBLs did not start to compress their sound at higher volumes. That is, while the sound stage, bass slam and air around the instruments on both the 301s and L-100s appeared, in the sweet spot, to be about the same, the 301 performance started to become noticeable when pushed hard with lots of power by not getting any louder. One area where the 301s excelled was that sound stage was wider - you could step out of the sweet spot for the L-100s and you could then tell when the 301s were switched back in as the sound stage expanded again.
The sales guys were completely impressed and used similar demo setups in their sales pitches on the floor and sold a _lot_ of 301s. As the bench tech, I was usually called upon to design and install sound systems for many restaurants, cafes and other smaller establishments. For these applications, I found the slanted-front 301s to offer lots of flexibility for placement and sound coverage. We installed many, many sets for this reason, too.
Clearly, the speaker's design center and product positioning was well-done as the product still sits in the product line some 40+ years later. This is a testament to well-executed, targeted marketing, IMHO.
Cheers,
David