Skywatcher'sSuper Plossls are amongst the lowest priced eyepieces available today at a mere £20. As such you could be forgiven for dismissing them altogether, if you did, however, you'd be missing out on an incredible bargain as each one of the SP series can outperform similarly focal lengthed eyepieces at three times the cost.
The 6.3mm uses 4 lenses (or elements) in it's design set out in a symmetrical configuration, that is to say in two groups of two tightly spaced lenses. Using only 4 elements in an optical system makes for clear and crisp views, generally speaking in the budget category using extra glass can only serve to degrade image quality. The price to be paid, though, is a 52 degree field of view which is typical of the Plossl design but on a planetary/lunar eyepiece such as this may become frustratingly restrictive
When observing planets or the moon at high magnification the object can move quickly out of the field of view meaning telescopes must be nudged and readjusted more often than when used with wider fielded eyepieces. If this is a problem you have two options, either buy an eyepiece with a bigger field of view or invest in a clock drive that will keep the object centered within the field of view.
Optically the 6.3mm performs very well indeed. Images are sharp and contrasty due in part to the blackened edges of the optical elements. Spurious light is minimal on the brightest objects and is far less than you'd expect from an eyepiece of this price. There is an element of image degradation in the outer fifth of the field but again far less than other similarly priced eyepieces.
As there are only 4 lens elements eye relief is a little tight and the objective lens is quite small, it's a toss up with this design between price and comfort. If you want a more comfortable eyepiece to look through you will have to shell out more money. While not very comfortable to look through this is a symptom of the design and focal length rather than an inherent failing on behalf of Skywatcher.
To conclude this eyepiece must be considered in it's £20 context, are there better eyepieces available? Certainly, yes, but for sheer affordability and an admirable optical performance, a short eye relief and pin hole objective lens can surely be overlooked. The 6.3mm is worth every bit of it's price tag and indeed more, it consistantly keeps up with £50 eyepieces in my collection.