Both of these wallets got the first decision right: no altcoins. That's the baseline. Now let's figure out which one actually earns a spot securing your bitcoin.
I've used both of these wallets. I know how they feel in your hand, how the software works, and where they cut corners. Here's the honest breakdown.
The Bottom Line
Both are solid Bitcoin-only choices, but Coldcard Mk4 edges out the competition with superior features and community trust.
Feature Comparison
The specs that matter for Bitcoin security.
| Feature | Coldcard Mk4 | Krux |
|---|---|---|
| Price | $178 | $40 |
| Bitcoin-Only | Yes | Yes |
| Open-Source | No | Yes |
| Air-Gapped | Yes | No |
| Secure Element | Dual ATECC608A secure elements (belt and suspenders approach) | None (software security) |
| Connection | MicroSD (air-gapped), USB-C, NFC | QR codes only (air-gapped) |
Under the Hood: Security
Let's get into what actually matters: how these wallets protect your bitcoin.
- Coldcard Mk4: Dual secure elements with extensive anti-tampering. Designed for maximum paranoia with duress features.
- Krux: Stateless DIY signing device. Similar concept to SeedSigner but supports more hardware.
Krux is fully open-source, inside and out. Coldcard Mk4 technically isn't. This matters more than just about anything else to me. With only "verifiable-source" firmware, no matter what a company says, there's ultimately a small layer of trust still present. Why not let the community gain full access? Open-source means anyone can not just look at the code, but build with it too. Blockstream hosts all kinds of DIY workshops at conferences to showcase the Jade's brutally transparent architecture. I know which approach I trust with my bitcoin.
Coldcard Mk4 supports air-gapped operation via QR codes. Your private keys never have to touch a networked device. Every USB cable, every Bluetooth connection is an attack surface you don't need.
Coldcard Mk4's Advantages
- Both are Bitcoin-only (good choice either way)
- Air-gapped operation for maximum security
- Fully air-gapped operation
- MicroSD for PSBT signing
Best for: Security-paranoid Bitcoiners, Users who might face physical coercion, Technical users comfortable with complex devices, Large holders who want maximum protection.
Krux's Weaknesses
Requires direct connection (potential attack vector). DIY assembly required. Less polished UX. No commercial support.
The Verdict
The Coldcard Mk4 is the gold standard for paranoid security. The duress features alone set it apart. But let's be real: most people don't need this level of protection. The UX is clunky. The screen is small. The numeric keypad makes passphrases tedious. If you're a high-value target or just paranoid, get it. If you want a smooth daily driver, the Jade Plus is more practical.
Price & Value
Krux is $138 cheaper at $40 versus Coldcard Mk4's $178. But cheaper doesn't always mean better.
Who Should Buy Which?
Budget-conscious? Krux costs less. Security-focused? Go with Coldcard Mk4. New to self-custody? Either will work, but start with the one that keeps things simple.
Common Questions
Is the price difference worth it?
The winner costs more, but the security features justify it.
Are Coldcard Mk4 and Krux Bitcoin-only?
Yes, both are Bitcoin-only wallets with no altcoin support.
Can I store other cryptocurrencies on these wallets?
No. Both are Bitcoin-only, which I consider a feature. Less code means fewer vulnerabilities.
Can I use my existing seed phrase?
Both wallets support standard BIP39 seed phrases. You can import your existing 12 or 24-word recovery phrase from any compatible wallet.
Full Reviews
Compare Coldcard Mk4 to:
Compare Krux to:
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