That hasn't been my experience with the Lowel kits at all. I have never seen the plastic knobs broken. The first things to go are the barn doors, umbrellas, and the light stands. The bulb filament can break if you drop the light. The rest is fairly difficult to break.

I've seen some of the metal parts in Lowel lights get warped out of shape... but presumably that can happen with any light. The barn doors, umbrellas, and lights stands are prone to breaking if you don't treat them properly.

2- I really like the 250W Pro light... you can get the ceiling scissors clamp for them and mount them from a ceiling. The light is small and lightweight enough that you can attach it to stuff in various ways.

Usually all the lights can more or less do the same thing. In this rare situation, the Lowel light can do something the other lights can't easily do (a polecat or boom would allow this).

3- For your purposes, I would aim to get a versatile kit. Not necessarily portable if you can drive your gear to your shoot. And because of your budget, I'd consider some of the cheaper solutions.

The gear I would look at is:

Cheap + useful:
Reflectors - simple, effective.
If you shoot outside, a mirror or two can be handy. The cheap way to do this is to tape tinfoil onto cardboard, and don't crinkle it. Get some sort of stand to grip it to (a C-stand would work, although there may be better choices).
Stands to hold the above in place.
All the misc. stuff listed in the low budget lighting article... i.e. blackwrap, extension cords.

Lights:
At least 1 soft light source. Chimera/softbox (rostronics/britek is the cheapest I believe... i.e. compare to Lowel Rifa), vic milt's nanolights. Bouncing a tungsten light into a reflector would work too. Open faced lights are good for this purpose, although just about any light will work.
Soft light is very good for lighting talent because it doesn't cause much shadows, is flattering, and generally looks more natural than hard light.

1 hard light for backlight. i.e. Lowel Pro, which you can mount from some ceilings with the scissors clamp (I don't think the Briteks can do this).

1 light to light the background. Hard sources can be good because you can cast lighting patterns onto the background. Soft sources are good if you don't want shadows on objects in the background.

One combination that would work would be the Britek kit (with 1 soft box), a C-stand + grip arm + grip head, all the misc. stuff (CTB gel, blackwrap, etc.), and make your own reflector (tape crinkled tinfoil to cardboard). By bouncing one of the lights into the reflector, you can have 2 soft lights + 1 hard light. That can be used to light many situations.

*I haven't used the Britek stuff myself.

Sorry, I didn't realise this is what you were getting at. I suppose it varies enough for me to not be able to specify anything more accurate than "people". That said, I prefer two-shots to singles so I'll often have to light two or more people in one shot. I use houses as locations usually (no sets whatsoever). I have written off the need to light exteriors, relying only on sunlight but I may find this doesn't always work. ie: Night time. I plan to do a lot of exterior night time shooting for my next project.

Depending on what type of work you need the light kits for ,I made up some frames to hold gells and barn doors on 500watt work lights .For most doco or short film sets they work just fine.