Installing any extension can lessen your overall Browser security - so make sure you download from a known and trusted source. Best to use the browser recommended addons and then look at the comments to see the stability and any potential issues.

In terms of the User Agent - this is an old technique used by some websites to change the website page content depending upon the browser being used.

Some websites that have been implemented with specific browsers in mind block access to browsers it doesnt support. Usually the less used browsers are affected and changing the User Agent is a way to fool the website (if its been poorly programmed) to believing it is a supported browser that it is serving its content to.

It will not affect your overall browser security - google chrome is well sandboxed anyway.

You can use an extension to change the User Agent on a per-tab basis. However, since v17, Chrome has this capability built it.

Let me show you...

press CTRL+SHIFT+I to go into developer mode.

Click the Settings symbol as shown.

Expand the pane as shown and click the Override User Agent tick box

Choose the user agent you want to emulate.

Close Developer Mode via CTRL+SHIFT+I