I am concluding — “low-noise built-in mics” not needed for bootlegs
Two things -
The noise floor (everything present on the recording that's not the music you intend to record) in a concert environment is way louder than the noise inherent in the device even for using relatively "noisy" mics like the ones built into portable recorders. The crowd, the HVAC system, wind, environmental noise etc is going to be there and can't be avoided.
You want the system you are using to be "low noise" but recording concerts with a device with factory mics built in is going to be similar no matter what device you choose. The built in mics in portable recorders are not top quality or they wouldn't be able to sell the device so cheaply. What many consider a "good" mic could cost hundreds or thousands of dollars.
If you adjust your expectation of the result to be in line with what you used to make your recording you will likely be happy with what you get. Pick the device that has the features you want the most - size, battery life, media format and of course sound - but do be aware that a lot of those recorders are very similar and better results are more dependent on the sound at your recording location than the device itself.
Recorder A that costs $400 in a crappy sounding location won't sound as good as Recorder B that costs $150 in a good sounding location.