Often times API or websites rate limits certain amounts of requests per minute. In multi_curl() this causes problem. A built in rate limiter would be extremely useful in such cases. Guzzle has something called guzzle-rate-limiter-middleware

Probably will be like:

MultiCurl::perSecond(3); // Max. 3 requests per second

MultiCurl::perMinute(5); // Max. 5 requests per minute