It's a highly portable version of a very specialized diagnostic tool.
If you're using the 12-lead by itself, you don't care about portability (as you're in a doctor's office or hospital). A 12-lead on a wheeled cart is just fine.
If you're using the 12-lead in a situation where portability matters (i.e. the back of an ambulance), then you need a lot more than just a 12-lead. You need something like a Lifepack 15, which combines an ECG with all sorts of other monitoring equipment (auto blood pressure cuff, pulseox, capnography, defibrillation capabilities, etc). An LP15 is not cheap (a mid-level version costs _5_ times as much as the last used car I bought), but it does what it does very well, and packs a lot into a small package.
Of all the factors considered by people who purchase things like 12-lead ECGs, price is often well down on that list.
All that being said... Would I buy one for $110? In a heartbeat.