I don't have any serious reasons for a downer on the Tessel. I'm sure it is fine if it fits ones needs. From the Espruino FAQ http://www.espruino.com/FAQ
- Tessel 2 has more memory (64MB vs. 64kB)
- Espruino uses a lot less power so it can run for years on a battery
- The Espruino Pico is much smaller (the original Espruino board is only a little smaller)
- Tessel is faster
- Tessel has WiFi built in (but you can plug WiFi or Ethernet modules into Espruino)
- Tessel provide pre-made modules that can be plugged in for certain things - Espruino's emphasis is on using standard hardware that's available cheaply from a variety of vendors.
I have a bit of a personal leaning to Espruino because:
- Esprunino runs on other devices. I have it running on my STM32 F4 Discovery development boards.
- The Espruino Pico is tiny.
- The Tessel is basically Node.js running on a big MIPS SoC chip. I already have Raspberry Pi and others if I want to move up to that scale.
- The earlier Tessel did not have a JS engine but rather converted your code to Lua. This seemed a bit clunky to me.
- The Tessel is a complex thing, not just a single STM32 micro-controller.
- Espruino is available now. I have two here. Tessel is on pre-order.
Still, if you need all the RAM space and extra speed of a Tessel it may be just what you want.
I may get one myself for comparison.
Memory in C++ is a leaky abstraction .