Just some general observations here, with regard to that next paraglider winch you might be looking for!
First, a general point about safety. Much like paragliding itself, the safety of using a tow unit of any type really boils down to the attitude and training of the people involved.
Having said that, if you could analyze the stats you would most likely find that static towing is the riskiest. All it takes is for someone to take their eye off the tension.
Using a stationary winch is better than static, as it's easier to focus on how the launch is going. It could also be argued that the control of tension is more precise as well, assuming a well-designed paraglider winch.
And the safest of all, most would agree, is the payout winch. It's basically idiot-proof, since the human factor is removed from the monitoring of tension. Mind you, there is still the possibility of someone setting the tension too high.
Interestingly, I came across one paraglider winch that allowed a combination of both payout and payin operation. But I don't see the need to elaborate on that here.
As mentioned in another page, the information available for doing it yourself is scattered far and wide. It can be quite frustrating trawling through the forums, magazines etc. looking for that ideal winch design for your paragliding operations.
Perhaps DIY is not such a great idea these days, unless you have a real flair for engineering and will get a lot out of the process of creating and testing a paraglider winch! The point is, it takes real skills and patience. Patience because some components just aren't readily available. And at the end of the day, the costs of quality materials these days can make the final product just as expensive as if you had bought it.
This is particularly true if you attempt to copy one of the latest commercial designs. It's hard to compete with the guys who are pushing out dozens or hundreds of units, since they are making a business of it and are finding ways to minimize their costs. The real cost if you DIY of course is time plus material costs.
Moving on to the home-grown winches now. There is plenty of safe towing done with these winches, the product of enthusiastic practical people. Many of them have decent mechanical engineering backgrounds. When you find some of these for sale, it will be clear that this is the cheapest option.
For a long time, since the earliest days of paraglider towing in fact, most winches fell into this category. Even now, there are probably more of these than the commercial units. I can see this changing in the future.
Not surprisingly, there is great variety in size, weight and performance between these independently-developed winches. Also of course, some are stationary while others are of the payout type.
All things considered, using a 'home-grown' paraglider winch can be a good option, if you bump into the right people. You have to meet a lot of paragliding types to find one. After all, not everyone tows. You could meet them on or off-line. Paragliding school contacts maybe. Or paraglider shop staff might know someone.
If you find a decent second-hand winch, it would be a good idea to actually see it in operation. Learn from the experience of it's previous operators.
Despite the rather high capital cost of a commercial tow unit, there are long term savings and conveniences to be had with these. As plenty of well-run clubs or schools have found out, a state-of-the-art paraglider winch can be quite cost-effective over time. Largely because of the high number of launches that can be achieved in a day's operation.
These units tend to last longer, and are often more flexible in their operation. After all, the company selling them is trying to shift as many as possible! For example, they might make it easy to mount the unit many different ways. Or perhaps operate it remotely, and so on.
Being produced in most cases by professional engineers, the strength/stiffness vs weight of these units is likely to be very good. Hopefully they learnt something at uni.
You can expect excellent support from the most visible companies, since they want you coming back for more. For example, to buy other kinds of paragliding gear such as such as towlines and tow bridles.