I recently purchased an Icom ID-51A.
I was looking out for this radio, having decided quite a while ago that I really wanted a D-Star handheld, but the IC-92AD had already been in the market a few years and I was convinced that Icom must have its successor in development.
The 51A looks and feels great in the hand. It exudes the quality that I've come to expect from Icom.
I also own a Yaesu VX-8R, which I still think is an awesome radio. It too has a similar sturdiness and naturally I'm bound to compare the two.
I've heard the 51A is selling very well for Icom, which suggests that it is appealing as a product - and possibly that it is also seen as enough of a step change for existing customers to upgrade (like me perhaps).
The radio is pretty feature rich, as you'd expect for its pedigree - and its price (it's by no means cheap!). I'm not going to go into listing features here, but I'll offer a few comparisons and observations vs the VX-8R from the bit of operating I've done over the summer - including during a week's vacation on Vancouver Island.
The first difference to highlight are the available bands. The VX-8R supports the usual 2m, 70m bands, but also has 6m (requiring the attachment of an short antenna extension). In fact, much to my delight the radio also operates on the 1.25m band. So you have a quad band HT there.
The 51A meanwhile sticks to the bread and butter 2m and 70cm bands.
Whereas Icom strongly adopted D-Star as a product differentiator and has build out the technology across its entire product line, Yaesu has eschewed this technology. It's too bad that the big boys have to play this game, but it is what it is. To its credit though Yaesu have embraced APRS in their VX-8 line of radios, which is a feature very much worth having in a handheld. True packet radio APRS is really the only way to go if you want automatic beaconing with position and status reporting. D-Star has grown a position reporting feature using the 1200 bps data channel that is available parallel to voice, however, it cannot be used on repeaters in automatic mode as beaconing would interfere with voice communications (unlike the use of the dedicated 144.390 frequency for APRS beaconing).
Of course, the VX-8R has no equivalent to D-Star when it comes to digital voice (DV). D-Star really is an awesome thing when you consider the relative ease and convenience of doing routed voice calls across the entire world via the already very significant network of D-Star repeaters. Yes, there are other repeater linking systems out there (e.g. IRLP and EchoLink), but D-Star is much lighter weight in usage and is controllable with relatively nice UI instead of obscure DTMF controls.
Talking of DTMF, this is an area where the VX-8R has an advantage. Icom clearly wanted to tidy up and declutter the radio controls on the 51A and in this they did a pretty good job. The menu system and the few dedicated buttons that the 51A possesses are well designed and pretty intuitive (although any radio takes time to learn). However, in simplifying the controls this much, Icom have elided any numeric keypad and therefore there is no direct way of 'dialling' DTML tones. Instead, you can somewhat clumsily set up DTMF sequences that can be played back from the menu. I suppose this is fine for common repeater access and controls, but there's no way you could fumble your way through this in the 'heat of the moment', so to speak.
A final observation is that I think I find the provided antenna on the 51A a little sub-par. It's very compact and I'd guess that it's not very 'gainy'. It doesn't seem to do the job of the antenna on the VX-8R. I don't know whether the 6m extension on the 8R does anything for the gain on the higher bands, but in any cae the 8R's provided antenna is longer and seems superior to the 51A's standard fare. Consequently I have now bought a comet 'high gain' 2m/70cm whip for the 51A to use except when I'm clearly wanting something more compact.
So, at the end of the day, I tend to think of the VX-8R as more down-to-earth and workman-like. Both radios are pretty IMHO. The Icom menu system is much better than the VX-8Rs (although the latter is adequate, it's certainly not as intuitive IMO). For me a big clincher is the D-Star support in the 51A, although I had absolutely no luck getting into a D-Star repeater with the standard antenna while I was on holiday. I suspect I would have had more luck on the new whip, but that's not an experiment I can repeat easily. I have heard similar grumbling from other 51A owners - often in terms that they could only produce or hear "R2D2" (e.g. digital gobbledegook produced by digital stream errors).