The longer version
There are two different doors here, and most reviews of parental control software only talk about the first one.
Door one is the settings. This is the one every tool has an answer for, and the answers vary wildly. A lot of free blockers store their list the way the browser stores a bookmark and put no lock at all on the page that edits it. The button that adds a site and the button that removes it are the same button, one click apart, in a menu your child can open. Nothing gets hacked. Your child uses the feature.
In Parentech that door is locked. Removing a site needs the PIN. Opening a blocked one needs the PIN. Changing any switch needs the PIN, and the dashboard locks itself the moment it is closed rather than sitting open behind a tab for the rest of the afternoon. Your child can read the whole list without it. They just cannot edit it, which is the arrangement you want: a rule they can see is a rule you can argue about at dinner.
Door two is the extension itself, and it is the real one. Chrome keeps a page listing every extension installed, with a Remove button next to each. That page belongs to the browser. No extension can hide itself from it, block it, or put a PIN on it, because Chrome deliberately gives extensions no way to interfere with Chrome's own settings. Any product that tells you otherwise is either describing something it does to the whole computer, or it is not telling you the truth.
So the honest answer is that the lock is not software. It is an account.
The five minutes that actually fix it. On the computer your child uses, give them a standard account rather than the administrator account. On Windows that is a Standard user; on a Mac, a Standard account; on a Chromebook, their own sign-in rather than the owner account. Install Parentech in their account, sign in, set the PIN, and then keep the administrator password to yourself. A standard account can still browse, still do homework, still install nothing that matters. What it cannot do is remove an extension that an administrator installed for it, or install a second browser to get round the first one.
This is worth doing whatever tool you end up using. It is the single step that turns any of them from a preference into a rule, and almost nobody's setup guide mentions it, because it is a five-minute chore rather than a feature anyone can sell you.
What you would actually notice if it did go. Parentech is visible on purpose. There is an icon in the toolbar and the block page has its name on it, so a missing extension is a visible absence rather than a silent one. On the family plan, each computer checks in with your console about twice a minute, and one that stops reporting shows as offline with the time it was last seen. That is not proof of anything on its own. A shut laptop is offline too. But it is the difference between finding out on Tuesday and finding out in March.
There is also a smaller lever worth knowing about. From your phone you can close the settings page open on a particular computer and force the PIN to be asked for again, which is the right move when you can see a child is sitting in front of the rules with the dashboard open. It is not a substitute for the account fix. It is the thing you do in the ninety seconds before you get home.
That check-in is also the thing free does not do. On one computer, free is the whole product: every rule, no caps, changed at that computer with your PIN, forever. What the plan adds is reach. The second laptop. A different set of rules on each. And your phone, so the answer to "it is off and I am at work" is thirty seconds rather than the drive home. If there is one computer in your house and you are usually next to it, use the free version and keep your money.
What this does not reach
- A computer where your child is the administrator. Nothing on this page works if they hold that password. Fix the account first; the rest follows.
- A different browser they install themselves. Which is the same problem wearing a different hat, and the same account change closes it.
- A reinstall. Removing Parentech and putting it back clears everything on that computer, rules included. It is not a way past the PIN, but it is a way to start from nothing, and only a standard account stops it.
If the extension has already gone once, the walkthrough is here: they deleted the extension, now what. More on how the PIN holds the rest: Block websites.
Related questions
Will my child know it is installed? Yes, and that is deliberate. Hidden tools do not survive contact with a curious eleven-year-old.
Does it work if they sign out of Chrome? Yes. The rules sit on the computer, not in a Google account, so signing out changes nothing.
What happens if I forget the PIN? You sign in with the Google account that set it and choose a new one. No email, no support ticket.
What it costs is one page and no surprises.