Lowel lights are fine, but they are limited. They do not have particularly large units and they are not very versatile. They are generally open-faced (unlensed) lights that are good for bouncing off umbrellas, walls or white cards, or for pointing at specific spots with a bit of diffusion on them. Far more controllable is a fresnel-lensed light, which are units offered from companies such as Arri, Mole-Richardson and others. Lowel does have one fresnel light, but it is nothing to write home about.
Lowel lights are also a bit finiky and delicate. They are great for the private owner who will deal with them personally (read: gently) and they are physically quite small and light which is very convenient. But they certainly are not the end-all be-all lights and something like an Arri light kit would be more useful. Of course it is also much bigger, heavier and much more expensive.
I don't want to completely criticise Lowel lights. I personally own seven of them (4 Pros, 2 Vs and a Rifa55), but I also know their limitations.
Btw, Lowel is based in Brooklyn, NY, and they will repair their gear for FREE if you drop it off or mail it in to them. I think they do charge sometimes for certain replacement parts, but I've beaten my stuff to hell & back over the years and have taken gear over there a few times and gotten everything back better than new (model improvements over time) and have never been charged a cent.
Arty, I have been using Lowel lights for over 20 years, and for my application they are great. I am almost always a "one man" operation, so lightweight instruments are important to me. Also, if they break, I'm the guy who broke 'em...you won't find them in many rental houses because they won't stand up to much abuse. And next to many other instruments, they're cheaper to buy and I've never paid for a repair. All of the above makes a pretty good deal for my work.
I use the DP (500w), the Riffa light box (750w), the Pro Lights (250w) and the Lowel fresnel (650w) most often.
I do have K5600 and Mole products, and they are wonderful. But they are also heavy and expensive.
How you use your equipment should be an important factor in what instruments you need.