BA drivers is tendency to have a lot of third harmonic distortion (and to lesser extent 5th)
The ER4SR is <0.3%, Multi BA is <0.1%, ER4XR <0.6% for total THD at 1KHz. The ER2XR which is just as hyped at 94db is 0.7% at 1KHz before you that bring up
they decay pretty fast and have problems with timbre similar to criticisms of planars but don't sound like planars - the bass extension isn't as deep, it just don't slam or punch you with air (there are of course some exceptions).
How is that a con?, This is like giving a PC monitor a 2.5/5 for being 2ms but give a 32ms 1080P HDTV from 2012 a 5 star impression for gaming.
Electrostatic > Planar = BA >>>> Dynamic if we're being realistic. I've got a ER3XR & getting a ER4SR later on but I've had zero issues with bass the 4SR with 6db sounds just as full as any other bassy IEM wither DD or multi BA, The Detail is big jump too I can hidden things in music that would be hidden in many DD headphones/IEM's. Gotta love the ones jumping in to say avoid BA drivers are the same ones who never tried one and are just parroting views as if they're total fact.