There are 3 disadvantages to using a high magnification.
1. Not enough light
2. Field of view too narrow
3. Shallow depth of field
If you are looking at large bugs, leaves etc... then the minimum 40x magnification will cause issues with all 3.
1. With my microscope, the light comes in from underneath, so anything that is not transparent (or semi-transparent) will be black, so (for example) its no good for looking at detail on top of a bugs back.
2. You could not see the entire bug (if its large), only small 'silhouette' sections around its edges.
3. It would be impossible for the entire bug to be in-focus. You could focus [say] on its head or its legs, but not both at the same time.
A high power microscope is really for examining thin transparent sections of things. For example a drop of pond water will show many little critters that are far too small to be seen at [say] 10 to 40x. But they will drift in and out of focus as they swim about. To solve this you use a 'cover slip' (a very thin piece of glass on top of the water drop) to keep it flat and in focus. These little 'critters' are so small that the bottom light source easily shines through them. For this I use about 100 to 400x.
A lower power microscope (like the one in your link) is ideal for the larger stuff. However I don't see any light source on the one you linked. They normally require some form of 'gooseneck' or 'ring' light that clamps around the bottom objective lens, that provides the overhead illumination. At 7x bright room lighting might be sufficient, but as you increase the magnification the view will get much dimmer (over 40x darker at maximum magnification).
My answer to the "which one" question would therefore be "both". However you will find that either one can see 'enough' (be it the large or small stuff) to keep you busy for many years!
The low power zoom microscopes I have used at work typically magnify by about the same zoom range. They are very good makes (e.g. leica / zeiss etc...) and are very sharp at all magnifications. We do have a few of the much cheaper models and the downsides are :-
1. The eyepiece field of view is either narrower or slightly fuzzier at the edges.
2. The overhead light source is not as wide or bright and tends to be the 'goose neck' design, with the issue of not staying where you leave it (a bit like a cheap telescope mount - you aim it a something and when you let go it shifts slightly).
3. The zoom eyepiece does not keep the object in focus when you zoom. With the better models you zoom in, focus and then it stays in focus at any magnification.
4. The image quality gets a little softer at the higher magnification settings, but considering the low cost are still acceptable with regards to reasonable image quality.
Note: For magnifications below about 10x a simple magnifying glass will suffice. The main issues with simple magnifiers are the short working distance (as you increase the magnification) and poor image quality at the edge of the FOV.
You can also get a low power 2x microscope objective for the 40-1000x models (but you would need to check the microscope has the standard RMS thread on the turret).
With regards to the gaps in the magnification question... Its not been a problem for me... My microscope also comes with a zoom mechanism. It works by raising the eyepiece in a simple tube arrangement and gives about a 2x zoom range (obviously you need to re-focus if you adjust it). However I never use it! - But (as they say) YMMV.
One other thing you could do is get [say] 15x eyepiece to use with the 10x, this would narrow the gaps in magnification (or accept the small drop in sharpness and use the included 25x).
I have not used the microscope that much looking at pond life plants and bugs, so I must defer to the book? you have been reading. If that covers the specimens you are interested in and suggests a 7-45x stereo microscope, then that is the direction you should probably take.
However I am finding higher power (40-1000x) microscopes for as little as $50, so I guess there is not much to loose in getting both types.
Edited by andycknight, 13 April 2018 - 04:04 PM.