Firstly this is a solid-feeling and well-designed piece of kit. Upon receipt I was pleasantly surprised at the quality considering I got it for <£10 at the time. One thing I did do before purchase was to go to the manufacturers website and e-mail them to check the dimensions of this product including the depth of the lip as I wanted it to support my Headway EDB-1 Pre-amp which I use to amplify my violin.
The dimensions were quickly sent (Good customer service!) and are L:30cm, W:12cm, D:2.5cm - These *should* be added to the product description along with Max/Min bar sizes for the clamp.
For reference The EDB-1 is about the same size to the Baggs Para DI, the Orchid DI, and other similar products. It has instrument inputs at the 'bottom' i.e. the front edge and has balanced outputs on the 'top' and also a 1/4in. line out on one the right-hand side. The other side is flat with no I/O. I asked for measurements of the tray because I wanted to ensure the sides of this tray would either a: Not foul the side output on the pre-amp, or preferably accommodate my L-shaped 1/4 in. Jack plug when plugged into the side of the EDB-1. In use the Pre-Amp sits comfortable on the tray length-ways with cables in at the front and cables out at the top however I could have still used the side-output with at least an L-shaped lead.
With all of that in mind the product supported my pre-amp very effectively and it was wide enough with shallow enough sides that the cables did not get fouled. There is plenty of space on there for bits and pieces like capos, plectrums, etc and the shelf is solidly constructed. Were you to use this for a tuning/bypass pedal and/or EQ pedal or similar I expect it would easily fulfill your need as long as you didn't want more than one or two 'standard' small pedals on there including linking patch leads. You would have to measure your kit to check if it would fit sideways or long-ways and to see if there would be room for power leads.
The clamp itself is a smart design - Certainly new on me but seems very secure; there is a clip which has rubberised jaws which attaches to the microphone upright and then there is a screw built in with a flat plate which pushes against the ends of the clamp to help compress the jaws and hold it firm (As shown by the zoomed image on the main listing). It felt solid when secured to a Microphone Stand. With this in mind a standard Mic stand or chunky music stand (Conductor style) would be fine however I have not tested it on a 'student' narrow music stand upright. I suspect you would need to pad the jaws to enable it to work with this. Some of the rubber inlays you get with bicycle lights would be ideal although It would be helpful if the manufacturer added a 'Maximum and Minimum Bar size' as a guide as you could not use this with speaker stands but may be able to attach it to some table legs etc depending on requirement.
I did not have a need to check what angles it would work at when clamped but there are not adjustments so you need something vertical to attach it to if you want a flat surface to hold your kit.
All in all I'm very pleased - I awarded 4 stars as I have only test-driven the item a few times and haven't tested it to capacity yet!