Regarding whether they are recommended or not, for the security of your trading and funds, we always advise choosing a broker that is already regulated by a credible international regulatory body, namely: CFTC, NFA, FCA, FSA, FINMA, MiFID, ASIC and FMA.
A credible regulatory body is one that has been tested and is internationally recognized, and imposes strict sanctions on brokers if they are found to have violated agreed-upon terms. The regulatory body is also responsible for the security of client funds.
So please check the regulation of the brokers that offer zero spread.