Using modesty blocks to hold shelving - good or bad idea?

[OM2]

I have a small room that is 90cm wide.
Depth of shelves will be 44cm.
I want to put wall to wall shelving.
I need 'plastic bits' on each corner of the shelf.
2 screws to go into the wall and one to go into the shelf wood.

I searched loads and found what I wanted: Modesty Blocks.
Are these OK for what I want?

The shelving will be used for food storage.
So weight won't be heavy weight.

Important: the back wall is a main brick wall, so will be secure there.
But the sides are just plasterboards - but have tiling over.
(The original plan was to turn into a small bathroom. But we decided not to do that. The pipes for water usage are all there.)
I'm concerned about the strength of the screws into the wall for that part.

I do have a hollow wall anchor device that I bought some time ago (that has never been used!). Should I use that?

I can't find anything bigger than a modesty block for what I want.
Can I get them bigger?

EDIT: after posting, I saw some videos on youtube where guys used slim wood planks as shown below. Would this be a better than to use modesty blocks?

Thanks.

 

[securespark]

Yes, I would do that. Modesty blocks are not meant to support a great amount of weight.

They are mostly used to fix Contiboard.