A couple of size comparing shots of ha-2 and xd-05, for anyone who's interested.
I'd like to also add a word of my impressions, after owning ha-2 for half a year, and xd-05 for just over a month. Ha-2 is easily 2x bigger than xd-05 and noticeably heavier, so, if portability is among your top priorities, ha-2 might be your best bet. SQ wise, I feel xd-05 has edge in two ways. Ha-2 sounds slightly on the bright side for my ears, while xd-05 is relatively neutral and balanced. However, if you are into young female vocals, ha-2 may sound more appealing, because it has an emphasis in the up-mid area - to my ears anyways. Despite of the slight difference in sound signature, I am very happy with both driving my UM PRO 20. However, for full size headphones, in my case AKG K7xx and Hifiman HE400i, it is more obvious that xd-05 does a better job than ha-2. Full size phones just sound a little dull when pairing with ha-2. Well, both make full sizes sound less exciting comparing to a decent desktop DAC/AMP combo - mine are Teac UD-301 and Schiit Valhalla-2. But xd-05 does have more energy than ha-2. Connectivity wise, I will definitely give my vote to ha-2. It literally connects to any player with a USB port and just works. All cables you ever need are included too. On the other hand, xd-05 only works with computer out of box. You do need to pay a little extra for a OTG cable, in order to connect to Android devices, and pay quite a bit extra (~$40) for the camera kit, in order to connect to iDevices, which does increase xd-05's owning cost. I'm an Android guy, with a cable inventory, so it's not too bad.
I bought my refurbished ha-2 from Oppo Digital directly for $240, which I consider a great deal for its SQ and features. But if I had known xd-05 existed at the time, I would buy xd-05 instead, I think. My xd-05 was bought from Gearbest, brand new. They have it on sale for just over $150 shipping included - a unbeatable deal if you ask me. I think the sale is still on. For $150, you simply won't go wrong.