Should I use Public proxies even if I have 30 private proxies?

I was wondering if I should use the public proxies that are scraped by GSA if I already have 30 private proxies. Would improve the success rate or will it just take more time and makes things worse for me?

Thanks

No, never use public once if you have private I would say.

One method is that you can use the private proxies for google related stuff like index checking and public proxies to scape. This way you will not burn your private proxies

Private and public proxies can compliment each other. Please note that public proxies burn out fast as the number of people using the same proxies are large.

One good tool is GSA Proxy scraper. I believe it has 5 days trial. you can download and check if it is useful for your strategy.

Yup. The proxy scraper is amazing. Got over 300 working proxies to scrape. 

Unfortunately not many know about this tool (we do no marketing though).

In fact I have Im adding many sources to the tool all the time. One major source are forums where proxies are posted. Some have sub sections for proxy tools and programs.
I am reading them all and it's amazing how much crap you find there. All people rely on a hand full of the same tools who are really awful in speed, gui and functionality. I guess it needs time till people realize what else there is.

Since we are on this topic, I had a tangent question. 

Is it a good practice to scrape URLs yourself or I should just purchase from one of the SER lists provider that I see here on banner ads?

Well the people here sell there lists to you and others.
Advantages: - many URLs, fast and quick results
Disadvantages: - many others use the same sites

I would buy a list as a start or from time to time update mine and still scrape my own.