Some consultant firms are good, some are not.

Searching a good one if you want to go this way. I was a consultant for about one year. It was really good opportunity for me to grow as a professional. It had cutomer service training and took care of all of immigration issues.

If the offer is good and the firm is good, go ahead.

By the way, if you already had PERM and I-140 approved, you are eligible to renew another 3 years after your 6 years H1-B.