Your copy length should be based on 3 factors:
- The Product: the more complicated your
product (more features and benefits), the longer the copy. Box of
matches is an easy product. A heatmap tracking software is a
complicated product.
- The price. The more your product costs, the more
information you need to provide. If something costs $1, people
don't need to think much. If it's $10,000 they'll take weeks to
research.
- The Purpose: What's the goal? Generating a lead for a
service business requires less detail, but an ad that aims to make
a sale must overcome every objection the potential buyer may
have.
If you go for the for the long form, remember
that you don't need to put all of the information on the same page.
You can create sub-pages, it's okay to move supplemental
information onto a different page (layer, popup, etc.) and just
link to it.
For instance, Amazon often hides full technical
information of products behind a link-since it's only interesting
to the hardcore tech savvy customers (and most customers are
not).
The important thing is that all the
information needed to make the decision is on a single page. Don't
make people click to read stuff that you want them to read anyway
(like features, benefits, testimonials, pricing,
etc.).