Pros: Tonally similar to its predecessor yet packs in that last ounce of oomph, slam, musicality and finesse in just the right spectrums of audio. Worth it!
Cons: The black casing and hard-to-read words are subjectively not in line with the trademark IFI looks, but the sound makes the cosmetics tolerable!
Went into the shop to audition the original Micro (my current desktop setup) vs the BL. Remember, not all reviews here are about the BL but the iDSD Micro platform products in general.
Anyway, after an hour of careful volume-matched auditioning, what skepticism I had about the minor tweaks in componentry over the already-great-sounding Micro silver had melted away.
I have concluded that the upgraded components really make that last ounce of difference in an already fine product! Bass slam that was already pretty good in the original, is now more pronounced and adds to the oomph and color and the low end. Overall clarity, already good on the original, is now slightly increased and subtly smoother and sweeter. Overall image width and height, on the Senn HD599, is about the same to me, but then, with the added clarity+sweetness+slam, that same stereo image suddenly snaps into sharper focus on good recordings. On bad or average recordings the BL actually makes the music tolerable due to the added musicality. Ahhhh... musicality... that is the one elusive trait which could justify giving up my beloved Micro. The BL definitely has a palpable increase in musicality which I didn't even know I was hungering for, til today. The original silver Micro definitely has that muscical quality, but I guess the BL has nailed the fringes of diminishing returns down.
For new owners who have never owned the Micro but like its sonic signature, this more-expensive unit may be a hard sell because the we're talking about mostly the same features and hardware platform. For the price difference you get a couple high-end components and improved clock... can this super tweak really justify the price difference? To that, I now say YES, if extra slam and musicality make a pronounced difference to the kind of music you like. For most general listening of lossy music, the BL won't be justified over the original Micro. But with the right equipment that has the resolving power to let you discern the 5% increase in sound quality, playing high quality uncompressed well-recorded audio, that 5% suddenly scales to 10% or more. Really hard to put a finger on it, but I guess this kind of sonic tweaking is what drives the audio hardware-modding market worldwide.
For owners of the existing Micro looking to sell off their unit for this upgrade at the new price, I would advise a long side-by-side audition at the shop with your own gear in tow. The price differential you pay has to justify the improvements I mentioned above. Not everyone will feel the need to upgrade, if the music, other hardware and taste in audio do not require (or do not resolve the fine differences) the subtle increases in clarity and smoothness. Many headphiles depend on differences in tonal signature as the way to size up a tweaked product. In this case, the tonal signature remains unchanged, so that may give us a hasty conclusion about the value of the tweaks. But then again, anyone who owns the silver Micro (and bothers to keep it) would likely not be casual music lovers who go for V-shaped tonal signatures... so even a 5% improvement in an already good product can mean a lot if it is centred around not just tonality but the harder-to-define areas such as microdynamics, slam and musicality. The wonderful home-trial policy of IFI is definitely a good excuse to give the BL an extended spin in your own audio setup. Just don't blame me if you find the sonic improvements mild and yet you still decide to keep it because the music now somehow seems to connect with you more than how it did on the original Micro!
Oh, and one last thing -- the XBass and 3D features have been judiciously used to liven up flat sounding recordings on the original Micro, and I walked into the store today not expecting much improvement in the XBass+ and 3D+. In fact, I did the bulk of the audition without these features, so that I could get a good feel of the basic audio differences in the main hardware. But when it came time to test out these two features, I can honestly say, they really have been fine-tuned to sound more natural without losing much of the punch! XBass is now even tighter and more refined due to the main benefits of the hardware tweak on the bass spectrum. 3D+ is sweeter and more holographic at the extreme HF region. It makes the previous 3D now sound a bit harsh and brash (that sounded gooded nevertheless!).