Photos are not required, and many reviews don't even have them, so if the review is detailed and complete, I would never vote down based on lack of pictures or based on any detail in a picture.
That said, in reviews I love pictures! Many pictures! I have thought the same thing before about toy comparisons, that it doesn't help much if you don't have the other pictured toy. But again, I would never vote down because of it. There have been some memorable toy comparison photos recently, and I especially think the photos that compare several glass dildoes are really pretty.
I think that the toy comparison photos would be useful to some people, especially if it's a similar toy then there would be some who own it. The problem could easily be solved by including a ruler or some common object along with the toys.
I also think that suggestions like that are helpful and I always welcome them. I think a private message is the nicest way to send a suggestion, and the person receiving the suggestion can take it or leave it, no obligation to follow the advice or to agonize over it.