I am looking at making the transition from topping lift to boom kicker or rigid vang this year.
The topping lift gets in the way while under sail (chafes the luff)... it works great to hold the boom up, but that extra weight aloft is not helpful either.
These kickers should work well for your Cal, just be aware some booms aren't perfectly shaped for the "standard" kit. Mine for example has a "lip" on the bottom which prevents directly attaching the bracket (catalinadirect makes a boom kicker custom kit for it).
But generally, if your boom is nicely round, and there is room at the bottom of your mast, and you already have a vang, then a kicker is a great addition. Keep in mind you'll want to move the mainsail halyard to the aft end of the boom once you secure the main... Also if you are this acutely aware of the problems related to the topping lift, you'll likely want to remove it completely from weight aloft. The price you link to seems quite good.
A boomkicker completely supports the boom for a VERY short period of time, when the sail is down, and you haven't moved the mainsail halyard yet to the aft end of the boom.
The ADVANTAGES of the boomkicker are easily seen when you are in extra light air, it allows the boom to come up some to keep the shape of the lower portion of your main (more draft). A topping lift can be used the same way, but in my experience that usually happens in variable air... and you need the top lift for a bit and then not...
A boomkicker HAS to work in conjunction with a vang. The vang works against the upward force of the boomkicker.
As an alternative to the boomkicker/vang combo, is a rigid vang. Garhauer Marine Hardware -7211578