I had the same debate, finally decided on the Ultrex, and glad I did. Best money I ever spent on a boat accessory.
I thought the power poles would be a better option in shallow water but I only spend about 1/2 my time there. My impression is that you spend more time in shallow water based on your location. You can use the spotlock in shallow water, but if you are close to your casting target, I would be concerned about prop washing the target spot.
Another negative is that the spotlock will locate the front of the boat but it kicks the back of the boat around if there is no wind or current to orient it. In this regard, I make sure the boat is stopped or drifting backward before engaging spotlock to avoid the motor making a backwards correction and kicking the rear of the boat around.
If you are a cast length from your target, this is not significant, but if you are pitching or flipping a bedding fish, it could spook them.
A feature I use more than I thought I would is the iPilot. Working down a bank or weed line, I engage iPilot and set the speed on 2 or 3. This frees me up from the pedal and allow me to move around the deck for comfort or better casting position.
My Ultrex works great for me, and I would make the same decision again, but I wanted you to be aware of some possible negatives in shallow water.