I have a number of pieces of Behringer gear that I use in non-critical applications. The biggest disadvantage of owning Behringer gear is that of having to deal with the Behringer-haters when they see what you're using.
Behringer is just another option. FWIW, I see no evidence that they're illegally copying anything except physical appearance. Just because a Behringer mixing board looks like a Mackie, or a Berhringer pedal looks like a Boss or an Electro-Harmonix does not mean that the guts are identical or even strongly similar (beyond providing mostly-equivalent functionality).
Behringer is all about mass-production. They keep their costs low by using inexpensive labor and extensive automation. I don't know if any of you have ever been involved in creating a mass-produced product (I have), but there's a lot of expense and overhead beyond R&D. FWIW, R&D expense as a percentage of product cost is normally very low; even if Behringer was copying designs literally, they're definitely not saving enough money by doing so to be able to sell product at 1/2 to 1/3 the price of the name-brand look-alike.
I don't know of any company that starts with a completely blank slate when developing a product. There are remarkably few true innovators, and a lot of copy-cats. In every industry a lot of successful businesses climb upon the shoulders of those who have done the true invention.
Implementations of devices based upon prior art can't be patented, nor (as I understand from my research) can circuit board layouts be copyrighted. This latter point was from a court ruling in the Behringer/Mackie case; this may be the reason why Mackie settled with Behringer under undisclosed terms.
I've done some research regarding the lawsuits. As far as I have been able to tell, Behringer gets sued for trademark and trade-dress infringements. Behringer reduces their marketing costs by exploiting visual similarity. When they make a look-alike product they piggyback on the marketing efforts of the name-brand manufacturer. The consumer is already familiar with the features and benefits of the name-brand product. So long as Behringer delivers comparable functionality, the user now has a choice of acquiring a strongly similar product from two different manufacturers at two dramatically different price points.
A lot of people cite Behringer for having questionable "business morals". These people are unclear on the function of a corporation, which is to maximize profits. A company will tout "soft values" such as morality, eco-friendliness, community service, etc. only to the extent that such actions are perceived to increase profits. Corporations have a long history of breaking laws when the cost of fines and legal battles is less than the increase in profit as a result of the illegal activity.
It seems obvious to me that Behringer consciously and deliberately exploits trade-dress similarities for some (not all) of their products. As I noted earlier, this is a good strategy to take in order to avail themselves of the product marketing already done by other companies. This strategy may cause concern for the company which developed the "donor" product, but is not a priori illegal. It is a matter for the courts to decide whether the similarities are strong enough to grant remediation to the plaintiff.
Although I have singled out Behringer for this commentary, it is only because of the (unfairly, IMO) vociferous nature of the complaints against the company. Behringer is far from alone in pushing the limits of trademark and trade dress similarities. Take a look around at the products in your home, in your place of business, and on the roads. Notice the strong similarities of products created by different manufacturers. If you pay close enough attention, you'll begin to discern who are the innovators and who are the copycats. In almost every industry the copycats have a reputation for creating second-rate product which nevertheless sells like hotcakes thanks to the lower price point. This is simply part and parcel of the lifecycle of innovation in the "free market". Stronger regulatory guarantees of product exclusivity would stifle innovation and hold prices artificially high.
Meanwhile, boycott Behringer if you dislike their business practices. But do take some time to look at other products you buy; research the history of the critical innovations which made those products possible, and try to learn about how your favorite company gained access to those innovations. I think you'll be surprised...