Why bother? Units is a free app and does the same stuff.
There are three apps called Units - the free one and the $0.99 one both do conversions, yes, but neither will do conversions on the level of Equivalence because they (and no other app on the AppStore) mimics its landscape mode. I'm not quite sure about how many units they have, but Equivalence's unit library is extensive (260+ units in 31 types) and is constantly updated at the request of users thanks to its over-the-air update system. The third app, which currently costs the same at $1.99, does dimensional analysis and comes closer to Equivalence's purpose, but (at least I think) lacks in implementation and design.
Some of my reviews describe Equivalence's pluses well:
"The basic mode works fine and is probably comparable to other unit converters. The advanced mode of this application is head and shoulders above any similar product I've seen here. The power is that it combines a calculator and unit conversion (including the ability to recognize and simplify combinations of units based on dimension). So you don't have to write down the conversions, then switch to a calculator." -
equivalence user
"A very good application with good use of iphone interface, easy to use and updated frequently. The missing units from previous reviews have been added. I spent two days one on one with the developer via email helping with an area I did not understand and was very pleased with results. Customer service of this caliber is hard to find these days." -
rbach
"This application strikes a good balance between power, ease of use, and flexiblity. The developer is very responsive and helpful -- that alone is worth the price." -
Traum1
...and there's a lot more like that, especially in international stores.
"A response to a request for extra "time" units was met within hours. Now that's service" - UK
"today i bought equivalence 1.0.2 through the app store. initial thoughts are that this will be the converter to beat. very slick interface and future releases will add more features among currency conversion." - Netherlands
I'd be happy to answer any questions you have about it, but I will say (despite my biased nature, and at the risk of sounding haughty) that the other conversion apps don't come close to what Equivalence can do.