There's nothing wrong with cave fills, at least the reasonable ones. I don't like pushing LP tanks past 3200 or so. I always found it amusing during my cave training that every single aspect of the training was dedicated toward safety..... except tank pressure.
The bigger question I have about whether you should buy those tanks ($200 is not really a great price, but isn't ridiculous either) is how tall your friend is. I used to dive with those tanks. I'm about 6 feet tall and they hit my legs when I kicked. The tanks are huge and heavy. Make sure they can be handled comfortably before buying them. Mine are now used only for banking oxygen.