I've been using the D1 Minis for around 6 months now. The only problems I've had is I got two of them that had something wrong with the USB and some of the Aliexpress shipments were really slow, like 6-7 weeks. That's out of around 25 I've bought.
I don't know about the range. I've only used them about 20 ft from my WiFi router. They just have a PCB antenna you definitely want to be careful about not blocking it with a metal enclosure or whatever. I'd guess you would get a better range with an external antenna. I have a couple of ESP8266 modules with the SMA connector for them but they're less common and I haven't seen a board with one. They also have modules with chip antenna available, there is a WeMos D1 Mini Pro that has one and more flash(though they haven't added that one to the ESP8266 Arduino core yet, maybe you can just use the regular D1 Mini board?). I'm not sure how much of a range improvement the chip antenna provides.
You should be aware of the difference between ESP8266 modules and boards. For example the D1 Mini uses one of the ESP-12 modules. The ESP8266 module is a circuit board with the ESP8266 chip, flash memory chip and the supporting passive components. Usually these components are under a metal shield. Usually there is an antenna also on the module. Other than the ESP-01, the modules have the contacts along the edge at a smaller than the normal 0.1 inch pitch and thus are not breadboard or prototyping board compatible. The boards such as the D1 Mini, NodeMCU, etc. add the USB circuitry and voltage regulator in addition to breaking the pins out at the standard 0.1 inch pitch. There are also boards like the WeMos D1 that have the Uno form factor so you can use the standard Arduino shields on them. The D1 Mini also has a variety of shields available.
You should be aware that the D1 Mini doesn't come with the header pins soldered on. This is actually a good thing because it allows you to decide which type of pins you want to use, male(to plug into breadboard or circuit board), female(for the shield), or male and female. They come with all 3 types of pins. It's very easy to solder them on with a little practice and this is something you'll need to learn eventually if you're going to get into working with electronics.