A rigid vang is probably double the price (even from Garhauer) and the installation would be a bit more involved. Installing a Boomkicker is a snap (1-2 h max, with no need to unstep the mast, remove the boom or sail etc.).
For Boomkicker, you need to add a vang, if you don't have one already (which may add to the cost (a couple of fiddle blocks plus extras).
so a rigid vang vs. boomkicker is a 6 vs 1/2 dozen (almost).
A question to those who switched from a topping lift to a rigid vang or a boomkicker: what did you do with the existing topping lift? Left it just in case (spare (emergency) halyard, secondary support when going up the mast?) or removed completely?
When I installed my rigid vang I removed nothing, except the old soft vang. The mainsail can be left folded on the boom. Garhauer fabricated the mast and boom bracket to fit perfectly. I was told what type of fasteners worked best... so I did spend another $10.... plus $7 for the correct size drill and tap... Total time for installation was about 1 1/2 hours... An experience person could install in 30 minutes or less.
As far as price goes... the boomkicker rod kit for a 25 footer will cost over $200. A new 4:1 soft vang with two double fiddles and cam cleat will cost around $120 (double that from westmarine). The larger 16:1 rigid vang I pictured earlier now sells for $495... I bought mine 14 years ago for 275. The smaller Garhauer rigid vang, 12:1, I think sells for 275 and is stainless... I would go for the newer model Aluminum R-6 ... priced at $375 and rated up to a 32 foot boat... really nice looking unit...
So installation is a non issue... therefore it comes down to price...and for less than a $100 more you can get an extremely functional piece of sailing hardware that is also enhances the beauty of you boat.
re: top lift question.... Mine was a funky static line with small purchase system and cleat at boom end. That static wire is now wrapped around the backstay and serves absolutely no purpose.. I'll remove it someday.... have forgotten the last three times up the stick... not important. I use the main halyard clipped to the boom end for stabilization. Got rid of that infernal boom pigtail, though.