Не поддерживает JavaScript, обязательно требует регистрации на стороннем ресурсе. И, главное: в бесплатной версии - только одно сканирование в день ("Sorry, but for using this period you have to upgrade your subscription. Do you want to upgrade now? No worries we have 7 days free Trial") и не более пяти подписок ("Current usage of your subscriptions - 0 out of 5 wachets."). Хотя, в описании про платность услуги ни слова. Не люблю я таких способов продвижения, основанных на сокрытии информации и по сути обмане.

Useless does not work with javascript. Is there any proper working web monitoring software that works with javascript?

Dear Anon,
You dont need a program to SAVE OFF SITE..
Have it save on your computer, Either during the day or WHEn you turn your computer ON..

Why have a 3rd party?

While it offers a free service, it's limited to only one scan per day, unless you pay. For comparison, Update Scanner for Firefox and VisualPing for Google Chrome offer user-end scanning that can check every 5 minutes. To go even further, VisualPing offers a server-side scan as often as once every hour (for free), which is still 24 times more effective than what this extension offers.

Simple tool if you need to keep an eye on web page or it's part if changed. Great that checking is happening on Wachete service so you don't need to have PC running. Their free plan includes 10 pages every 1 hour. Mobile apps are also super helpfull