From what I found they may have some benfit on the appearance of scars. But the info available is contradictory.
It is featured in a article on ncbi.nlh.nih.org called: Snake oil for the 21st century
Effect of Mederma on hypertrophic scarring in the rabbit ear model
Computer analysis of the scar photographs demonstrated no significant
reduction in scar erythema with Mederma treatment
A New Proprietary Onion Extract Gel Improves the Appearance of New Scars
once-daily application of the proprietary advanced formulation of
onion extract gel is safe for use on new scars and significantly
improves their overall appearance, redness, softness, and smoothness
compared to control scars.
Hypertrophic Scarring and Keloids: Pathomechanisms and Current and Emerging Treatment Strategies
- States that available data is contradictory
A comprehensive evidence-based review on the role of topicals and dressings in the management of skin scarring
Two randomised studies by Draelos in 2008 (n = 60) and 2012 (n = 44),
following shave excision of seborrheic keratoses, concluded that
Mederma® improved the appearance, signs and symptoms of the healed
wounds compared with untreated controls [42, 43]; however, both these
studies note that funding was provided by the manufacturer Merz
As for the Amazon product I cannot find where it was sponsored or approved for safety.