Products with konjac don't have any contra indications: the only indication is that it is preferable not to take more than three grams per day, as it is a fiber that is very challenging to the intestine.
And the general rule of good sense is, to limit the amount of product eaten on a daily basis and, especially when the product has not yet been tried, introduce it in small amounts. Like any new food!
The other important rule is to drink enough, especially children often drink too little water: make sure that they drink when they eat foods with konjac!
Risk for choking for people with swallowing difficulties or when eating with inadequate liquid.