Jason is correct. The Intelliflo is not designed to be like a standalone pressure-side pump that produces up to 50 PSI (about 115 feet of head) at a low flow rate (say, < 25 GPM). At it's maximum RPM of 3450, at 20 GPM it produces 94 feet of head, or 41 PSI.
I just got an Intelliflo (and IntelliTouch) and wanted to get rid of my dedicated pressure-side pump running a Letro Legend cleaner. I looked for a cleaner that was designed to run off the returns at lower flow (and pressure). I, too, have a dedicated 1.5" line for the cleaner. I found
The Pool Cleaner and my PB told me he was at first skeptical but tried it in his pool a few years ago and is still very happy with it. So I got it and it does work, BUT I found that with 3 returns plus the dedicated return for the cleaner it doesn't make sense to run the cleaner at the same time as the main returns. I tried having mixed flow, but even The Pool Cleaner really needs a dedicated or near-dedicated flow to it -- it has too much resistance which will just force the water to go elsewhere (if it can).
So my current setup has the valve that turns the cleaner on simply redirect all flow from the 3 returns to the single cleaner line and I have my pump set at it's lowest of 15 GPM. The cleaner in this mode is actually a little on the high side of its recommended wheel RPM, but seems to clean better and it's not getting overflow from the pressure relief valve. Worst case, a SMALL amount of diversion to the other returns would be OK, but I find things to be far less consistent where there are other paths the water can go (the smallest pressure blip causes a lot of flow to divert and I think that results in not quite as good a cleaning method). With The Pool Cleaner, the pump runs at 15 GPM, 2180 RPM and 540 Watts which isn't too bad. With the cleaner off and going through 3 returns, I could be at 15 GPM, 1175 RPM, 155 Watts but I'm set up to do a single turnover over 8 hours of daytime and 3 hours of cleaner time later at night (I'm thinking of reducing it to 2 hours since it's cleaning so well) so am at 24 GPM, 1400 RPM, 232 Watts which is still really good. When my solar is on, I'm at 48 GPM, 2980 RPM, 1500 Watts which is still better than my previous pump, but I've set a slightly lower flow rate so slightly lower solar heating efficiency (my previous pump was probably at around 52-54 GPM).
My biggest worry is that the Intelliflo isn't letting me prioritize the custom flows and instead if more than one custom feature is on at a time, then it just uses the largest of the flows. So I HAVE to run my cleaner at night and can't share the daytime because if the solar turns on at 48 GPM but the cleaner is running with all flow to its single dedicated line -- well, you can imagine what will happen. Probably the pump will get to its max RPM and then shut down, unable to achieve flow (and the pressure relief valve at the cleaner outlet will be propped open a lot, I'm sure!). There is a "Master Cleaner" setting that can be used with the cleaner which will shut down the solar when the cleaner turns on, but it only does that for 5 minutes so does me no good so I just run as "Generic" and have a regular filter program on during the cleaner time (perhaps I'll change my mind about this -- not sure yet).
Anyway, I'm happy with my current setup. I hope it works for you (though it does mean getting a new cleaner). Quite frankly, I was fed up with the Letro Legend anyway since the bags don't close well anymore (I had just got a new one less than a year ago) and parts get broken now and then. The Pool Cleaner has far fewer moving parts and the bag is much better designed with the velcro part on the side rather than the top, so it tends to stay closed better. Well, at least so far. The company is located in Santa Rosa which isn't far from where I live so worst case I can complain in person if there are any problems.
One thing to keep in mind is that The Pool Cleaner uses a much fatter 2" (I think) hose compared to the Letro Legend. It comes with an adapter for the return line. The good news is that it has a very easy twist removal so taking the hose and cleaner out is very easy (we do that to maximize swim area -- it doesn't stick out that far, but we're picky).
Richard