What about the temperature ?

Yes. I installed it, a CIQ field but it seems that Explore 2 has native support without using any CIQ field.

something is fishy with temperature logic, so if device is in stand by , then temperature is starting from 21 C, then in next sec its rising like from 21 to 29 C, where other devices displays like 26 

I dont care that much , but its very strange behaviour , and its not acurate (at all)

I tested my edge 1000 and 1040 in a thermal chamber, against Pt100 sensors, and *my* 1040 is faster to respond and more accurate than *my* 1000.  Sample of one, your mileage (or better, your temperature) may vary.

Edge 1000:  -3C error, tau 6.25 min (time to reach 63% of step change)
Edge 1040:  +1C error, tau 4.23 min

This was done on forced air controlled temperature chamber and compared to calibrated class AA Pt100 RTD sensors.

They can certainly still improve response time (so every ride doesn't take 15min to go from indoor to outdoor temperatures), accuracy (for a $600 device expectations are higher), resolution (sensor likely has better resolution, or dithering can be employed, or at least low pass filter in transitions) and pickup point (insulate it from device, couple better to ambient air, eliminate 'sun on black device'  effect).  I offer to help, if they read this.

That said, it was improved from *my* 1000, and 1 degree temperature error and resolution will not detract from my enjoyment of biking. Not a gearhead (just a nerdy engineer).

I'm surprised to see it's accurate. Mine will always read 10-15F over reality, in or out of the sun. It also constantly goes up and down even sitting on the table inside my house. 

Eventually I removed the temp data from from my screen as it only served to annoy me.

If yours is that much off, get it replaced under warranty. 10F off is not acceptable.  My test was on my 1040 vs my 1000, I was glad it improved, but in a dark chamber forced air performance,  Could be that in the sun it cooks hotter.  My 1000 would start to show display polarization issues in the bottom center above 103F (and I would be melting away at Henry Coe park, too).

I have Windfield and Temp fields on my screen. Windfield reported temperature was 72°F, and Garmin displayed 96°F. I mainly rode in full sunlight, and it was a warm day (for Germany), but the temps were not out of the 70s and nowhere near the 90s.

OK, got a Tempe to try and compare.
In the thermal chamber, both are very similar all the time in steady state, but
1. Edge 1040 big chunk of metal slows down changes, minutes to settle to new temperatures - affects start of rides and rapid changing temperatures
2. Edge 1040 still has only 1C resolution - even if not accurate, 0.1C resolution would be nice to have. Someone can actually create a data field that either generates it from moving averages or records from internal available. Tempe records 1 decimal, even in F (should always record to fit in C, for consistency with existing temperature field.
3. The main difference is impact from sunlight into the unit - it can be dramatic, I saw +10F in the last ride.

Given that, it is potato, potahto, some people might prefer just to use the internal and know it includes the sun factor (which affects the user as well), or deal with the extra tempe on different bikes, connect IQ, yada yada. At least on the 1040 the Tempe Data Field CIQ logs every minute to the fit file, and Garmin connect shows as a plot at the end of the ride.