AdaFruit and SparkFun both provide MCUs, sensors, and other peripherals that integrate well. Couple that with copious libraries and example projects and you may be up and running without having to stare at data sheets and wiring diagrams and JTAG output just to (say) get a temperature reading and display it on a tiny OLED screen.

All of that plus maintaining inventory nearer their customers, doing effective QC on units they ship, writing good docs, etc. means you’re getting something a lot more like a “big OEM” experience from the hardware vendor, even if you’re ordering a handful of parts.

The generic AliExpress vendors, in my experience, do not do most of those things. They all support Arduino and/or PlatformIO, and sometimes a “native” SDK like mbed, but you’re often on your own figuring out how to integrate that bare MCU with other devices you need for a complete solution. Docs are often incomplete or untranslated, and it can be hard to know exactly which chip (or associated components like onboard sensors and BME) is on there. It can change between board revisions, or even identically-named parts from different vendors.

There are other players like M5 and RAK who make nice modular platform as well, but their prices tend to be up there with AF and SF.

Both Adafruit and Sparkfun manufacturing quality is higher than generic manufacturing from China. I suspect that most of the Chinese alternatives meet their price point by using parts that are out of spec and were purchased at a discount by the chip manufacturer (or just scrounged for free from the reject pile).

My primary example is this clock generator breakout: https://www.adafruit.com/product/2045

The board is open source and there are tons of options made in China, often on a purple PCB. I've had terrible experiences with them, over 50% of the purple boardss I've purchased fail to achieve PLL lock because of multiple reasons- sometimes replacing the crystal can get it locked, but sometimes the chip is just out of spec and can't get a lock. Occasionally I'll get a lock on one PLL and the board is partly useable. I've given up dealing with the hassle and now I just spend the extra few dollars to get a breakout that uses parts sourced from authorized distributors that meet quality control standards. Plus this gives the profits to the people who designed the board and released it as open hardware.

Adafruit products work as advertised, and are very well documented. Sparkfun is similar though their level of documentation is (IME) a bit more hit and miss.

For rando parts you get from rando vendors, it’s pretty common for schematics to have mistakes, pulldown resistors to be kind of off, and other components to be low quality.

For prototype development work, I’d rather spend a few dollars to have reliable parts that can be easily reordered than spend hours or days tracking down issues in parts that can’t always be reordered.

For post-prototyping and production work, you’re probably spinning boards anyway, and your choices and risks are pretty different.

For me, it's the Teensy 4.x boards. I have uses that consume all of their horsepower. I'm just a researcher, and my prototypes will be commercialized by an engineering team that will use the same microcontroller but on their own board and developed under their preferred auspices.

It's the closest I can get to an FPGA within my skill set.

Also, I think that Paul has been exemplary in his contributions to the open source community despite his own product having a closed component.

Adafruit in particular is very good at providing step by step tutorials on how to use their products, most of them that are nontrivial have a little example project to go with them.

It's also been a good one-stop shop, if you want a little character display to go with your esp32 project they will have one, along with addressable LEDs, battery circuitry, etc.

It's a bummer both sites are melting down

Olimex are a better middle ground than sparkfun or adafruit for the things they cover.

In truth people will spend a lot of money paying other people to shop on Aliexpress for them so they can maintain the illusion they are above all that.

Product support, documentation, comparability, and community support/forums

Adafruit dev boards are way more expensive than Chinese alternatives but I've never used an Adafruit board where I went "why in the world did they do X", where X is some design choice (except having a bright LED light up while the board had power). On the other hand I've had Chinese boards that have a battery jack but an always-powered component on the board uses like 10+mA at all times when alternative choices for the same component use literally hundreds/thousands of times less power (but cost 1 cent more).

> A lot of those come with very good support and communities as well.

Which ones?

I’ve dealt with Seeed and the quality of support falls far below.

Number one reason would be lead time. Adafruit always ships immediately and the transit time is short on the east coast.