I know Dartside well, used to keep my 4.0 Avon there...
It is a shallow slip. As others have said the challenge is pulling her out and up the slip on recovery - maybe after a long day on the water when you may be tired. I'd fit a towbar and use the LR, lot quicker, less strain on yourselves plus you can tow it round to the washpoint to flush the engine and wash her down etc..
It also gives you flexibility to launch elsewhere e.g. when tides are poor -Galmpton is only ok for launch / recovery no more that +/- 2.5 hours either side of high tide - you don't want to be stuck on the mud for 6 hours
Another advantage of a towbar is it does protect the ear of your vehicle from muppets who can't stop in time - it's saved damage to rear of my car at least 3 times when in queuing traffic people have run into me!