mare is correct. i think they called it 'hummingbird' because it is a compact form. i have this one and a couple more and i don't see the hummers on it. it is, however, the real butterfly bush! they, along with wasps and bees, love it(might not want to put it beside your back door *lol*).
it won't flower much at all in deep shade.
the fragrance is very nice.
the fall color on 'hummingbird' is nothing to write home about, at least not in the southeast. you may have better results in a colder climate.
the pink-flowered clethra called 'ruby spice' is a very pretty yellow in the fall.

Thanks for the encouraging responses! I suspected flowering might not be as good in dense shade. I have an alternate part shade spot in mind (it's only kinda close to the back door lol) I'm excited about watching a new type of plant grow. I haven't tried a lot of new stuff lately. You have me tempted to go back & buy the other one, ha ha. Guess I'll have to start collecting clethra now. Thanks again. Carla

Clethras are beautifully scented I think, one which you may want to consider getting also is clethra arborea(almost like lilly of the vally) but it's not as hardy as the others, such as barbinervis.

RP1

it look like the bush is dying

I have some in my yard, it blooms around mid summer with a wonderful fragrance, and turns a golden color in fall. It was 4' tall when I bought it 4 years ago and it is still 4' tall today.

I would like to keep this bush on the short side. Can I trim it, and if so when is it the best time to trim

Trim in early spring or after flowering. This will promote a fuller look, stronger branches, and more flowers the following season. To propagate, just take a low branch and pin it firmly to the soil with a heavy stone. Keep the soil moist, and it will send out roots. Leave it attached to the "mother" plant for a year. When roots have formed, cut it free and carefully dig it up. This is best done in early spring.