Inline heaters for whirlpool bath

I'm preparing to install a Jacuzzi Luxura 5 whirlpool bath. This is a 32" x 60" tub, not one of the big ones. I'm undecided on whether to install the optional inline water heater. The one offered by Jacuzzi, the RapidHeat unit, costs about $370 on the street, as nearly as I can tell.
So, two questions. One, can these be installed through the access panels after the tub is installed, thus allowing us to learn if we really need one at all? Two, are there cheaper generic inline heaters that would work?
I am pulling wires for the separate heater circuit just in case.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file
Upload is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.