These two are not the same kind of product, and the honest comparison starts there. Shelly EM is a finished, certified device you wire in and it works. rbAmp is a metering front-end module — you add current transformers and an ESP32 host and build exactly the meter you want. So this isn't "which is cheaper" — it's modular-DIY-and-precise vs turnkey-and-certified.
Read this first — what you're actually comparing A Shelly EM price is a turnkey price: the enclosure, the firmware, the cloud, and (on the EM Gen3) a CT in the box. An rbAmp price is a module price: you still add a CT (~$9/channel) and an ESP32 host. Below we compare all-in DIY cost against Shelly's turnkey cost — not the bare module price against a finished device.
The numbers
| rbAmp UI7 (module) | Shelly EM Gen3 50A | Shelly Pro 3EM | |
|---|---|---|---|
| Price | $18.99 | $69.99 | $154.99 |
| Channels | 7 | 2 (1 CT incl.) | 3 |
| In the box | module only | turnkey + 1 CT | turnkey + 3 CT, DIN |
| $/channel (module only) | $2.71 | — | — |
| $/channel (all-in) | ~$13 DIY (+ CT + host) | ~$35 | ~$52 |
| Accuracy | ±0.5 % / ch (0.5–18 A), guaranteed with factory-paired rbAmp CT · standard SCT-013: a few % out-of-box → ±0.5–1 % after a one-point calibration | 1 % Class B | 1 % Class B, IEC-certified |
| Host / integration | your ESP32 — ESPHome/Arduino/Pi, local | built-in, Shelly Cloud + local | built-in, Cloud + local |
Specs & prices checked: Aug 2026 — rbAmp: rbamp.com · Shelly EM Gen3: us.shelly.com/products/shelly-em-gen3-50a · Shelly Pro 3EM: us.shelly.com/products/shelly-pro-3em-us-list.
Where rbAmp is the better fit
- Cost per measured circuit. Even counting the CT and the ESP32 host, an all-in rbAmp channel lands around $13 against $35–52 for Shelly. If you are metering many circuits, the gap compounds — one ESP32 can host a multi-module rbAmp bus, so the host cost amortises.
- An accuracy guarantee Shelly can't offer. Here's the honest version, as a ladder. With a standard SCT-013 (manufacturer class 1 %), out-of-the-box accuracy is typically within a few percent — clamp-to-clamp variance, and clones especially, see to that. A simple one-point calibration against a reference (supported in all four rbAmp libraries) brings a genuine clamp to ±0.5–1 % on our bench — on par with Shelly's 1 % Class B. And the factory-paired rbAmp CT goes one better: module and clamp are calibrated together, so ±0.5 % of reading (0.5–18 A) is guaranteed for your unit — a per-unit accuracy guarantee a fixed-clamp turnkey device simply can't give you. (Figures are for resistive loads; we don't publish a low-power-factor number we haven't bench-verified.)
- Modularity & ownership. Pick 1–7 channels per module, put several modules on one I²C bus, read them from ESPHome, Arduino, a Raspberry Pi or ESP-IDF — no cloud, no subscription, no vendor lock. See the UI-series card.
Where Shelly is the better fit
- Certification. The Pro 3EM is IEC-certified Class B — if you need metering for billing, sub-tenant invoicing or an insurer, a certified device is the right tool; rbAmp is not certified.
- Turnkey. Unbox, wire, done — no firmware to flash, no host to choose, a CT already in the box on the EM Gen3. If you value time-to-running over cost-per-channel, Shelly wins.
- Polish & brand. Mature app, Shelly Cloud, a large ecosystem and support org.
The honest boundary
rbAmp does not yet ship an integrated multi-channel device — a multi-circuit rbAmp meter is a DIY build (module + CTs + ESP32) today. Integrated, ready-to-run units are in development. So if you want something that looks and installs like a Shelly, that rbAmp product isn't here yet; what is here is the module series that lets you build a cheaper, more precise meter yourself.
So, which one?
- Billing / certified / plug-and-play, a circuit or two: Shelly EM Gen3 or Pro 3EM.
- Many circuits, tightest accuracy, local-only, willing to build: an rbAmp UI-series bus.
New to CT metering? Start with How CT Energy Measurement Really Works. Coming from a Shelly or PZEM setup? See Migrating to rbAmp and keeping your Home Assistant history, or build one in 15 minutes with the Home Assistant Energy Dashboard guide.