Tens or EMS units

You've got the basics down already.  TENS is designed for pain relief, EMS is designed for muscle strengthening.  The main difference is their intent.  Getting into more detail, there are differences in the protocols used between the two, in terms of intensity, pulse frequency, pulse duration, wavelength type, and especially the placement of electrodes.  I believe TENS can be used by just about anyone with muscular pain (according to the indications/contraindications), but EMS is better used by people who have some sort of rehabilitation going on, for whatever reason, and have below-normal muscular strength; e.g. - you broke your leg and lost a lot of muscle while it was immobilized.  You won't see a whole lot of benefit, if any, by using EMS when you're healthy and strong.  Here is a good overview of EMS: http://www.biostimtherapy.com/newsletters/october00/ems10_00.pdf. 

(disclaimer - I don't know anything about biostimtherapy as a company and therefore don't know anything about their products)

You can find a decent portable unit of either kind for $100 or less with 2 channels.  I got myself a dual-channel TENS unit for about $40 on sale. 

Oh, and if all you're looking for is treatment of tight muscles and increasing blood flow, I'd save my money and use moist heat, like a wet towel put in the microwave or something like that.  Just be sure not to burn yourself.  Or ruin your microwave.  As always, check first with an MD, ATC, or PT for advice on your specific condition and treatment plan.

There is no physiological difference between a TENS Unit or an EMS Unit. Both will relieve muscular pain and/or muscle spasm. The only difference is packaging. Just my 2 cents.

Actually there is quite a difference between TENS and EMS, and also between different models in terms of results. What you wrote is equivalent to saying that the water dripping from a faucet is the same as the water coming from a shower. It is the same stuff, but different modalities and different results. For sport applications there has been quite a progress among hand-held professional units. You may want to read this review by a researcher who applies EMS in sport:
Maffiuletti NA. The use of electrostimulation exercise in competitive sport. Int J Sports Physiol Perform. 2006;1(4):406-7.  Also take a look at the titles in this bibliography.

Tens is a temporary pain relief unit. Only has a carry over of 10-15 unites of pain relief once it is taken off.

i agree with you