Why use a phone other than a MiFi or 3G router? Because an Android phone is far more flexible. For example, you can let the hotspot go through a VPN and/or proxy connection. And for $19, it is also far cheaper than any MiFi or 3G router.
There are two versions of this Concord II: T-Mobile and MetroPCS, their firmware are slightly different but compatible. I.e., you may flash a T-Mobile FW to a MetroPCS, vice versa. The one I got is a T-Mobile; so if any of the followings do not apply to the MetroPCS version, at least you can flash it to T-Mobile to get all the same functions.
First thing first with any phone is to root it. Fortunately it is very easy, just run a batch script:
Optionally, you may remove blotware, also explained in above link. There is a link to a MetroPCS FW too. A list of what I removed can be found at the bottom of this article. You may not have to remove anything, but some of them such as Lookout and SetupWizard might do very bad things under the backgroud to damage a smooth hotspot experience.
After root, we can run WiFi Tether Router to make it a hotpsot and it works perfectly with the default configuration without any tweak, see above photo. Experienced random disconnects (then reconnected by itself), changed from WPA2 to WPA then problem solved.
Chinese is one of the built-in languages; the other two are Spanish and English.
The only downside: no LTE. This is actually a good thing to me, because LTE is weak and slow in my area, saving me the hassle to disable LTE. So far this is the best hotspot I have had - the most dependable and the fastest.
[update] Xposed can be installed through the installation mode of recovery (flash zip automatically). Then Moto Tether module can be added for bypassing hotspot provisioning.
Bought an unlock code for $12 from phones.outlet on ebay because of 100% positive feedback. The code arrived after about 7 hours and worked (a metroPCS version).