According to the link above, not many of his original illustration paintings survive. But examples of his prints do. Below are some examples of each type of work.
Allen was a competent illustrator. However, due to the lack of images of his illustrations on the Internet, I feel that I can't provide a fair, comparative evaluation.
I wrote about this illustration here.
Apparently most of his 1920s illustrations were painted in oil.
He made many prints of construction scenes.
A particularly dramatic composition.
Exaggerated ... unusual for Allen. The caption I found on the Internet said he made it, but that might be mistaken.
Realistic, but Allen also was doing abstract work around this time.