I looked at one of the design links for a cnc router and felt, in consequence, the need, based on past experience, to utter a note of caution about purchasing design plans. While plans can be a extremely valuable and well worth their asking proce, they do not always satisfy and some degree of caution is appropriate.
The plans that I looked at had no component list to help one assess whether the design uses components that are readily available at reasonable cost in a potential users situation. I spend a lot of my time in europe --and would need one machine in europe and one in the US. Markets are different, available resources & components are different and measurement systems are not universal.
In my life time (I am almost 70 now) I have used many plans and designs. I would say 20% have been really good and 50% were cribbed rehashes of pre-existing designs. The worst 30% were often far too dependent upon proprietary components or used one or more difficult to obtain or totally unreliable components. Some were clearly based on a one off build and showed no signs of systematic revision. A high proportion of such designs were far from modular and were organized in a way that made modification extremely difficult.
If a designer is unwilling to publish the components requirement for a plans set then, frankly, I would not recomend a purchase. How does one know whether a redesign would be needed if, in a builder's judgement, specified components were unreliable or unobtainable?
I emailed the designer of the cnc router about this problem and I found the reply attitude to be unhelpful and lacking appreciation of the risks he was expecting the builder to run without disclosing relevant information to facilitate appraisal.
If a designer does not understand that a builder needs to be given an opportunity of determining whether the plans have a genuine potential for the builder, (and that must include the right to access a component list prior to purchase), then I say "beware".
Before buying "plans" take care to ensure that the designer does not see his component list as the transaction commodity. A good designer would not, in my view, rely on up front component list secrecy to sell his/her plans.
The value of plans lie in the way the designer puts components together and in the way he/she has designed the project to save you building time and other costs during the construction. The builder must be able to control material choices and a good designer will provide a detailed list of alternative materials and potential suppliers
A cautious prospective constructor can then obtain quotations for materials, assess the design potential from the designer's brief and on the basis of a cautious assessment determine whether or not to purchase the plans.
I have found designs from a designer who does not take the time and trouble to explain his design strategies are often unnecessarily complex and present unexplained and hidden challenges to a builder. If a designer expects you to pay for a design up front then expect detailed component lists and a design philosophy and introduction to be supplied as a matter of course in advance of handing over any of your hard earned money.
There are plan suppliers who expect prospective builders to take too much on trust. Some have allowed an apparent fear of being ripped off to get in the way of establishing a respectful relationship between builder and designer.
If a designer is going to give me the confidence I need to purchase his plans then I see a need for him/her to demonstrate, from the outset, an understanding that a potential builder has to be prudent and supply the information essential to make careful judgment.
Paying for unseen plans and finding out too late that to finish the project one has to pay too much money to acquire components or that components are not readily obtainable in your location, or that the design relies too heavily on a limited range of proprietary sources, or that the design gets in the way of using recycled components, is deadly. Unfortunately it is possible to become heavily committed before the pitfalls are realized.. then prepaid plans can be much more risky and expensive than designing from scratch.
That way at least your have to learn, in detail, about what you are doing.
Do not buy a pig in a poke. Proceed with caution and check that the designer is open-minded, helpful and has a good pre-sales appreciation of builder's concerns. Buying plans is an inherently risky option for a builder. A policy that enables a potential plan buyer to make a realistic assessment of those risks prior to purchase reduces those risks to an acceptable level. In my view an opportunity to examine the component list and a detailed write up of the design philosophy is essential.
If those things are present then there is a chance that post sales support might be there. Above all choose a designer whose prime motivation foes beyond the revenue stream and whose disclosure policies are generous and do not seem to be based on fear.