@juliea55 This is a really common question, and can be confusing. People use the same words to mean different things.

When people say “portable” nebulizer, they usually mean battery-powered, not just lightweight. In other words, it doesn’t have to be plugged into the wall while you’re using it. Most portable units are light and quiet too, but the battery is the key distinction.

Tabletop nebulizers are traditional plug-in compressor machines. They’re reliable but big, loud, and meant to stay in one place. The Ombra is an example.

The PARI eRapid/eFlow gets called portable because it’s battery-powered, but can also be plugged in an outlet. A lot of people use it at home as I do, and also take it on travel. People choose it because it’s faster and quieter than a standard compressor nebulizer. Treatments take less time. It's considered a mesh nebulizer, and does not have a compressor. It uses a vibrating mesh to create the mist. That’s why they are small, quiet, and fast. The downside is cost and that the handsets are recommended to be replaced every 6-12 months.

If you are considering the eFlow I'd urge you to search the forum here as there's been a lot of valuable information written about it, which is impossible to recreate here in this post.

A few links to illustrate the differences.
https://www.saveritemedical.com/products/ombra-120v-table-top-nebulizer-compressor-system
https://nebology.com/products/pari-trek-s-portable-nebulizer-system-with-lc-sprint (compressor based, takes similar time as tabletop)
https://nebology.com/products/pari-erapid-nebulizer-system-with-eflow-technology