[janoskiss (Steve H)]

As Adrian said they are GSO barlows (all Bintel branded gear is GSO). I've only had experience with the 1.25" 2-element 2x barlow (the cheapest one) and the 2" standard 2x and ED 2x barlows. They all perform well enough for the price. I found no difference between the ED and non-ED barlows.

Much of the apo vs semi-apo vs achro barlow thing is about marketing. An achromatic lens is all that is needed to make a good traditional barlow free from any false colour. An "apo" or ED lens may still be relevant in short high magnification barlows ortele-converters/extenders.

I have not tried the newer models: the 3-element 2.5x and 5x units. I am tempted to get one for planetary imaging because they are cheap. Most GSO gear is bang-for-buck and I assume these would be too. They don't make anything that is appallingly bad. You definitely get what you pay for and often more.

I don't think you need to worry about sharpness of images. They will be as sharp as seeing and your scope allows. Barlow lenses are easy to make and hard to stuff up (although some still manage to do just that uhmm meade and there are the obvious junk ones that you can tell by looking at them).

I used to own the 1.25" and 2" 2x GSO barlows, but I sold the optical elements from both and only kept the empty barrels to use as extension tubes. There are better barlows out there for more money. I suspect the GSO barlows can be improved by better blackening of the insides of the barrels and by installing baffles. Most of what I gained from more expensive, better made barlows can be attributed to better stray/scattered light control. If I lost all my barlows I'd probably just get a basic GSO and improve on it in the way I described.

I am very fond of my extra long 2x barlows (Orion Ultrascopic style. 1.25" and 2", fully-baffled, Japan made). I don't know if anyone makes anything like these any more. Long barlows tend to result in flatter fields and less off-axis aberrations. They can make an inexpensive EP perform very well in fast scopes. Most barlows on the market today won't do that to quite the same degree.