Exceptional Controller / Admirably Priced
The A-300 was purchased to replace an Edirol PCR-300, which it shares many of the same features/functionality, all updated (and with Roland branding).
If you are familiar with the PCRs, then you will have no problem immediately working with the A-300 [500/800]. I do like now that Roland added a bright 2x16 character LCD display, as the PCR's 2 character display was a chore to deal with.
Gone is the horizontal mix slider of the PCR and the dynamic pads have been updated with nice, thick soft rubber pads which really make a difference when triggering/finger drumming. The sliders, of which there are nine, have also been updated with hard-rubber mixing desk-like concave grips. The entire build quality is high and on-par with Roland's professional synths.
I use the A-300 in a Mac production environment, with Logic and Digital Performer as the main workstations. After the necessary driver installations, the A-300 paired immediately with Logic with preset factory controls [ACT parameters] - which were fine - however, i preferred to set up the controller in a way optimal to my working ideals, thus I created Control Maps specifically for these tasks. The Control Maps setup was identical to how the PCRs operated. Pairing with Digital Performer required the A-300 to be in a specific DP Control Map, but that was not a problem.
The A-300 functions as a MIDI Interface as well and I used it as a means to control NI Battery by way of the V-Drums and it works without any issues. Amazingly, the A-300 is entirely USB bus powered only drawing 300mA of power.
I chose the A-300 mainly based on my experience with the PCR and I enjoy the workflow presented by these Roland controllers, most specifically being able to immediately change Upper and Lower MIDI parts on the keyboard and instant Split and Dual - with memory recall. Switching Control Maps is quick and seamless.
I definitely have mixed feelings with Roland's pitch/modulation stick as I do prefer separate pitch and modulation as on other products, although it is not a deal breaker by any means. The keyboard has the same velocity/channel aftertouch synth action as Roland's V-Synth series, but semi-weighted would be a plus for a future product. Perhaps even a D-Beam too.
I would like to mention that I used, on a whim, the A-300 with an installation of SONAR in Windows 7 via Parallels in OS X and it is here where the full breadth of functionality of the A-300 can be seen. The A-Pro Utility in SONAR is incredible and would hope(wish) that Roland would provide this for Mac DAW users, as it potentially increases productivity in reassigning controls on the A-300 while within the DAW. If you are a Windows user, then this controller (at least with SONAR) is indispensable.
In conclusion, I would recommend the A-300 (or 500/800), it possesses impeccable amount of controls and superior build quality. By comparison, in addition to using the PCR series, I have also used controllers from M-Audio, Alesis, and Korg ( with the Korg Kontrol49 being one of my favourites of all time).