I have a Ultralieve home ultrasound kit. It helps me to recover from injuries quicker.

Most portable ones dont have the power and right wave length capabilities
Look for something with at least 1Mhz freq, capable of both continues and pulse waves

I recently purchased a $60 home ultrasound unit. This particular unit is called Model ProM-660, but there are many different "models" which look exactly the same and many others which look slightly different but mostly the same. This thing vibrates at approximately 120 hz. This is a little short of 1 Mhz (by a factor of 10,000). I can't tell you that it doesn't also produce a 1 Mhz frequency, but I find this 120 hz frequency highly suspicious.

I have also been reading about ultrasound therapy, and it appears there is very little, if any, quality research which demonstrates any benefit. Yet billions and billions of dollars of ultrasound therapy have been applied over the last 50 years. There's a sucker born every minute (actually it's 4 per second) and I am one of them.