It is always hard to direct someone with one unit over another as it is very subjective. A disclaimer I must give is that I like chirp, but I do not think it is the end all be all answer that is better than CW or frequency selectable ducers. It is better at some things, but not everything. I use these machines often so try to jump in on these threads when they come up and offer my experience.
The first thing I would do is forget the amp and get the DFF3-UHD network sounder. It is smaller and lighter than the amp and does the same job. You also are less restricted where you can put it. The amp has installation and distance requirements that limit where it can be put. My guess is the DFF3-UHD is going to be around for a while and will likely get more software updates along the way than the internal TZT3 sounder. That is just a guess. Price is the same and to me there is not benefit to getting the amp over the DFF3-UHD. I do believe buying the amp over the dff3-uhd may have possible future drawbacks.
I do not know if you have room to do this, but you could keep your transducer and add something like an R109LM. Now you have the HW covered for pelagics up higher, the M for bottom fishing/finding deeper pelagics/finding bait and the L for super deep performance. You would have all your bases covered. It is good to note that after a certain depth chirp transducers are picking a single frequency. To me chirp is less advantageous when talking about deep water fishing as it is acting mostly like a CW transducer depending on your depth.
I like the stand alone sounder machines for deep water if you are someone who is going to use bottom zoom/bottom lock and do adjustments with gain clutter TVG etc. I like chirp better for pelagic up high and inshore shallower water fishing.
FCV-295 benefits: better deep water adjustability and customization. You get an extra screen. You can run you current transducer on TZT3 screen while running the new transducer on the 295. (You will want to shut off the L side on the existing transducer and just use your Low on the higher powered transducer).
DFF3-UHD benefits: Heave compensation which is awesome. Newer chirp technology. Will most likely continue to improve with software updates (it is already great). Better target definition and performance in depths where it can take full advantage of chirp technology. Do not need to find room for another screen. This will do a very good deep as well, but is somewhat less adjustable and you cannot do as many split screens if that interests you. Adjusting it manually is just not nearly as easy as the stand alone machines in my opinion.
FCV-1150 benefits (I had to add this here.): Awesome machine, but it does cost more than two you asked about. It is a 295 with bigger brighter screen, heave compensation and ability to network to your TZT3. When networked it can be viewed on the TZT3 which is cool, but not really necessary.
