I think Mark hit most of the nails on the head. I'll also add that I chose a different way to control depth of field, and that's by upping the power level (with monolights) and using ND filters. With the monos, I have all the power I need to do anything from 1 person to a fairly large group of people, the freedom to choose any aperture I want using ND filters, and the ability to underexpose the ambient while doing so.

Using monos and an ND filter, I captured this at f/2.2 on a bright, sunlit day:

Samara & the Willow Tree by budrowilson, on Flickr

Of course, monolights aren't for everyone; they're generally more time consuming to set up, they require pure sine wave inverters and a large battery source, and they are indeed bulkier to haul around. However, they provide me with the freedom to be as creative as I wish without being incumbered with the limitations of a speedlight's power. There are also more modifiers specifically made for monolights than for speedlights (although a plethera have emerged within the last few years).

Honestly, I'd suggest getting a couple of used Nikon SB-24s from KEH and shooting only manual for the next three months. This will allow you to [fairly cheaply] figure out whether or not you want to invest solely in shoe-mount flahses while also nailing down your manual control skills. After that, you can decide if the benefits of monolights (more power/more choice in modifiers) offset the drawbacks of increased setup time, bulkier transportation, and external battery requirements.

As far as the Westcott products go, they all look fine. That said, I just purchased an off-brand Orb the other day. I'm sure the build quality won't be as good as Westcott's, but for as many times as I think I'll use it, I'm sure it'll be fine--especially considering the price. Now I just have to wait about a month for it to arrive from China...

Also, you may want to look at smaller light modifiers too. When you start down the strobist journey, there's a tendency to go as big as you can with your light modifiers (here's proof of that). However, when it comes to small flashes, I often grab my 15" collapsible softbox. It can be fairly soft depending on how close it is to the subject, but it's more often just a bit punchier--and it's a nice change from the creamy soft gradients afforded us by larger modifiers. There are also plenty of other sizes and cheaper versions on Ebay.