This is not the "garland" pose but the "toilet" pose. Mala in sanskrit means impurity (or excretion). If you observe a traditional Indian toilet, it does not have a seat. It has a hole in the ground connected to a cesspit. Mala means garland in Hindi. The original yoga texts were in sanskrit.

I like putting a block between my feet sometimes to get a really nice and deeper hip opener...the block has 3 settings so you get to choose just how much hip opening you want.

can one do deep breathing while performing this?

There's some broken code in the page. If you look at the source, the benefits are:
1) Stimulates abdominal organs like the ovaries and prostate gland, bladder, and kidneys
2) Stimulates the heart and improves general circulation
3) Stretches the inner thighs, groins, and knees
4) Helps relieve the symptoms of stress, mild depression, menstruation and menopause

the only thing that would open up is contrainsdications and cautions. no benefits shown.