Not a particularly densely-foliaged plant, although you can pinch and prune to create more density. Select young plants with tight, acutely angled branches if you want a hedge. Some varieties tend to sprawl.

You can grow Feijoa in the parking lot; i.e. it is amenable to almost any format...hedge, espalier, even topiary. The more you prune it, the more it grows... My question would be,,,why bother with Feijoa??

Because it's an evergreen subtropical that is well suited for 8b where most other subtropicals would fail

Because of the unique leaves and beautiful flowers it produces (with sweet tasting edible petals)

Because it gives fruit later in the season when most other things are done

Because they taste real good

Reason enough IMO

My next door neighbor did a hedge row of pineapple guava on our property line. Her side is not pruned while my side gets pruned as branches grow too far into my yard. Here is what they look like after about 3 years in the ground.

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As the pictures show, the plants are rangy and not as dense as most hedging material. If you have room to let the plants get large-ish, they work. They do bloom on new and old wood, so some pruning does not eliminate next year's bloom totally. Feijoas need summer water to look their best, if you are in a hot dry summer area such as Portland.

There are some smaller-leaved varieties which are used for clipped hedges. But for best fruit quality, you should get named varieties. Small-leaved varieties may be useful to pollenize plants intended for fruit.

Sometimes plants offered for landscaping use are seedlings.

Here is a link that might be useful: Feijoa fruit facts

I just searched Yahoo images with "Pineapple guavas as a hedge" and found a number of hedges shown. Brady