Certainly everyone has their own preferences; one person's bright can be another person's neutral, etc...
My previous speakers were S series Magicos (beryllium tweeter) before purchasing the Spendors, and to my ears that tweeter provides another whole level of detail and speed compared to the LPZ tweeter used by the D series (let alone the Harbeth). Things like snare drum and certain percussion with the Magicos was the most lifelike sound I've experienced at home. I was amazed after going to a some live events and then listening at home how realistic certain things sounded to me.
The main driving factor for moving on from the Magicos was poor or bright recordings could become too fatiguing over long listening sessions. Great recordings sounded awesome, but not everything I listen to is well recorded...
The first speakers I listened to after the Magicos were the Harbeth HL5+ and 40.2. The beautiful midrange and non-fatiguing listening was great. I can see why folks like them. That being said, I definitely noticed details and speed I was used to hearing in my favorite recordings that were not present or at least not to the degree I was looking for. The 40.2 could energize a room and I liked it but it is too big for my room.
The Harbeth dealer mentioned to me he knew a music producer who used both Harbeth and Magico based on what he was recording...
For me I found the D series a nice comprise between the two brands and for type of sound I was looking for. Not counting tone and detail between Harbeth and the other brands I listened to (which all offer slim towers), the other thing I noticed was I didn't think the side to side and back to front imaging with the wider Harbeth boxes was as pronounced. I can confirm the D9's disappear almost as well as my Magicos did in my smallish room, which is pretty impressive for a pretty large speaker.
To be fair as well, I've not heard the D7 and although the Spendor dealer said they sound like the D9 but with less bass, I've heard others say the D9 sounds different because it has a dedicated midrange driver that doesn't share any bass duties.