TOPPING EHA5 Electrostatic Headphone Amplifier Balanced 229Vrms - reviews - There are 3 reviews.

Works great
To begin with, this unit is what is commonly referred to as a transformer box: essentially a conventional amplifier (in this case, a Topping LA90) paired with a set of transformers to provide the high-voltage bias required by electrostatic headphones (580 V for STAX, which is the de facto official/unofficial standard for most electrostatic earspeakers).

It’s a great little unit and works perfectly well with my STAX Lambda SR-L700. I’m giving it four stars, however, due to Topping’s slightly misleading claim regarding the 700 V RMS output. In practice, the unit cannot sustain this level and will shut down at around 229 V RMS when playing a 20 Hz signal (as documented here: https://www.audiosciencereview.com/forum/index.php?threads/topping-eha5.42149/post-1712440).

That said, this is essentially a non-issue in real-world use. I have driven it to ear-piercing levels of loudness without encountering this limitation, whether on low gain at maximum volume or on high gain around the noon position (which is already unlistenable).

I would also note that this unit lacks dedicated headphone output protection and appears to struggle with a 10 kHz sine wave at high volume (see: https://www.head-case.org/forums/topic/28658-topping-eha-5/).
About the headphones protection, Topping argues that such protection is unnecessary due to the inherent resistance of the transformers, which is a reasonable point, though additional protection would still provide extra peace of mind.

Importantly, none of these issues have manifested in my own usage. Overall, this is an excellent—albeit slightly flawed—solution for powering electrostatic earspeakers, and it is very fairly priced for what it offers. For a fully solid state (here fully transformer driven) amp you would have to look at STAX existing offerings like the SRM1-mk2 or SRM353X to cite two common "affordable" amplifier, or if you want tube any offerings by either STAX themselves or more boutique ones that woo audio may sell.

Good entry-level electrostatic amplifier
This amp is a good match for my STAX Lambda SR-300 headphones. It drives the headphones effortlessly. Sound quality is outstanding, especially for classical music - every instrument is rendered with clarity and precision.

Works Well
I just moved to France and am setting up my sound system. I purchased this and Stax Lambda headphones for my new home audio system, and it works well and looks good. I can not compare it with the other electrostatic headphone amplifiers available for Stax headphones because I have not heard any of those available now, but this is a fraction of the cost and sounds clear and clean to me. I like the visual aesthetic (and the fake tube glow, which amuses me, but...I like it), and I am contented with this product's ability to drive my difficult-to-drive headphones.