Yup - you must try it before you buy it. Preferably for at least several miles, more than just around the bike shop parking lot. Nothing special about Giant's frame sizing. They have - I think - 3 sizes of compact frames to fit everybody. They do this predominantly to save costs of manufacturing. They believe that this limited sizing is good enough and people can use different seat heights and stem lengths to get a proper position. For marketing purposes, they say that this results in a lighter and smaller, therefore stiffer, frame. Of course this is offset by the 12-24 inches of seat tube you need to make the bike fit. On balance it probably works out to be no better or worse than a standard bike frame. I personally don't like it, but many people do and love their bikes.