I have never experienced eating fake eggs yet. I might be mistaken because the real and the impostor look really similar. I wish I am right cause eating fakes is dangerous. 
I compiled some of the harzardous substances that you might get in eating fake eggs. Good luck!

Calcium carbide. Hazardous when ingested, inhaled. an skin and eye irritant. Toxic to lungs and mucous membranes. Repeated and prolonged ingestion may damage certain organs.

It produce acetylene and calcium hydroxide upon moisture contact. Acetylene – a flamamable gas that might contain toxic impurities of hosphine and arsine. Ca(OH)2 – Calcium hydroxide is irritating to respiratory system to skin and risk of serious damage to eyes.

Sodium benzoate. It forms carcinogenic benzene when used in combination with potassium benzoate and ascorbic acid. Combination with certain food coloring is known to cause hyperactivity in children.

Food colorings. I never know the specifics but many petroleum based dyes can cause children hyperactivity.

Paraffin – It is edible but not made for human consumption. It is used for coating fruits, vegetables, candies and chocolates. It gives shiny appearance and prevents the lost of moisture.

Calcium chloride. It is listed as a permitted food additive in the European Union for use as a sequestrant and firming agent with the E number E509, and considered as generally recognized as safe (GRAS) by the U.S. Food and Drug Administration.The average intake of calcium chloride as food additives has been estimated to be 160–345 mg/day for individuals [wikipedia]. Why did they set a limit for safe food additive? Is it really safe?

Baifan. Also known as alum. Used as medicine but excess intake may cause irritation of mucous membrane of gastrointestinal tract, nausea and vomiting.

No health issues were found regarding the following as of date: