I use T2T with my eldest using the iPad, it's definitely not a true communication device. However for 1/20 the price(iPad and one year subscription compared to Dynavox, purchase with enough batteries to get through a single day), it's certainly worth exploring. We have been using this device for little more than a week with our eldest daughter(almost 5 years old). She suffers from seizures resulting from brain damage she suffered as a 16-18 week old fetus, we discovered the problem in her brain around 5-6 months when she began having seizures.
She has been gradually falling farther and farther behind most developmental milestones since about 6 months. Her fine motor and speech skills are only at about a 2 year old level, her gross motor skills, comprehension and learning/problem solving skills are at or above par, as such we no she has a lot going on upstairs but like most children with a brain injury she freezes up and has extreme difficulty getting out words when she trying to say them. We have been working on several methods of alternate communication including ASL(sign language) and PECs((picture Exchange Catalog). She has done well with a few routinely used signs but her signing is at best an approximation and is only understood by her primary caregivers as she lacks the fine motor skills to properly make many signs.
PECs has been helpful as she has a larger PECs vocabulary than sign as the same motor skills are used in every PECs word/request as every other... but PECs is an extremely slow and cumbersome way to communicate, worse yet, no standard PECs library seems to exist(although Board Book users have begun sharing their boards online). PECs certainly has it's place but it's a great deal of work to set up each page, editing pages is a pain and frankly some of the symbology used is only understood by the initiated and is useless in real world applications if your child tries to communicate with someone who hasn't learned the system(about 2% of the world), not unlike the limitations of sign.
Tap to Talk although not a comprehensive communication program has many benefits:
1. $$$$$$ Cheap as Borscht compared to Dynavox 2. Like a board book you can assign any real world picture to the menu 3. Unlike board books it can play your audio when a picture is pressed, this means Real World Applications, unlike PECs or approximated signs, your server at Denny's can actually take your childs order as she presses the Meal button and asks for pancakes, and the iPad/DS/Android device says "I would like pancakes please", then when the server asks what they would like to drink they can switch the the drink menu and select the picture of a glass of milk and the device says "Milk Please". 4. When your child runs into a scenario you haven't accounted for such as the server asking would you like regular pancakes or buttermilk and the child knows what they want but there is no picture to say "buttermilk" they can flip to the choices menu with a giant check mar for "Yes" and a similar X for "No", and as the server to repeat, the server will quickly figure out to say(most anyway) do you want regular pancakes(assume no is pressed), ok do you want buttermilk pancakes? then the child presses the check mark and the device says "yes" 5. Most important of all, you can customize all your own menus, if you ended up at Denny's today and realized you didn't have pancakes in the menu at all you could guide your childs order by putting them on the choices menu, and asking them pointed questions they can answer Yes or No to to determine their order, then as soon as you're done, or as soon as the order arrives, you can take pictures of either the order or the menu and you can upload and add these pictures along with your own audio to add to an existing food menu or create a Denny's menu for you child's next trip to allow greater and greater freedom and communication over time.
We have only had the program for about 10 days now, the biggest bonus we have seen has been a passive one. Although children with brain injuries tend to have difficulty getting out a word they are focusing on saying, our daughter has been speaking 4-5X the words she did even a week ago as she speaks the word associated with the images she is pressing. She is not thinking about verbalizing the word only about pressing the button and getting a response. It seems as soon as the pressure to communicate verbally is taken away she finds it easier to get out the words. This recent change has been accompanied by a near doubling of her use of sign(same signs used more often). Although this may not be the be all and end all of AAC, such impressive results in the short term bode well for many parent testing out this inexpensive program on a cheaper device like a DS or iPad out of their own pocket rather than spending months or years looking for funding for a Dynavox or similar device.
Best point I can give... If your child sees benefit from this software but plateaus with it's limited capability, you will have a resounding argument when the time comes to get funding for a more expensive and comprehensive device like a Dynavox. You can already show their ability to utilize the type of technology it uses to communicate, show they've out grown it and then generall bypass several of the usual steps in getting approved for funding, which often included offers of a funded iPad these days...