Cell phone text messages generally work well enough. There can be issues so patience is required and that makes them unreliable for urgent messages if you should have one to relay.
We used FRS for a couple of years and it never worked well for us. Range can be an issue, frequency overuse can be an issue, the person on the other end just not paying attention can be an issue.
People have touted the ad hoc networking devices here for at least the past two to three years in the hopes of building a critical mass. They have never reported back to us on the results after the ride so we have no data to share with you. The cost of the one you link is not hideous but neither is it cheap. Personally I don’t think my teammates would go for it given that text messages do work reasonably well. Without them my only motivation to get one would be to help the rest of you out. That is not out of the question but first I have to start hearing that they have been used and are working at RAGBRAI … and that preferably during the ride itself.