Well if you have good education, experience and good IELTS score that makes your CRS good enough for you to get a PR invitation, then no need to use any consultant.
Whole process has lot of rules & sometimes looks complicated but if you concentrate properly, you can do everything on your own. These forums & whatasapp groups are also very helpful.
And moreover it's difficult to say which agent you can trust.
So my suggestion is do your research properly & be active on these forums, you will be able to make it.
Sometimes the experienced consultant tells the trick which you can not even dream about.
Anyway, filling incomplete application with immature information often closes the path for ever. Because the wrong information sent once (refused application) can not change/modify for future compete application . Everything is recorded.
If u r capable and and want to be successful in any condition. There is no harm.
I can suggest a honest Sask best consultant for SINP.