In my opinion, I prefer the red guard method. I think it’s a much cleaner approach to sealing a shower pan, bench and all walls. Using the standard “pool liner” as I like to call them also is a great way to seal a shower pan, but sometimes it’s difficult to get a smooth corner.
After experiencing a failure many years ago, I don’t like to trust “red guard” type roll-on membrane alone for shower pans or any area with standing water. For waterproofing around shower transome windows, or the upper corners of shampoo niches, etc, it works great if properly and thoroughly installed.
For a walk in shower, I recommend your installer use Schluter or NobleSeal membrane products. Like the Precision mentioned, the PVC liners don’t like to lay flat on the inside corners with the folds etc.
From my experiences Schulter Makes a product known as kerdi membrane and shower pan assembly with a drain. Hands down the best product I have ever used. There are several YouTube videos showing the installation method. To this day I have never had a leak and recommend their products.
I prefer to use the Schluter System. I have done many shower systems over the past 10 years, and never had one fail. I also found it as a time saver going with Noble Niches for niches. They do not work for all applications, but if you can find the size your looking for they work great. I am also a firm believer in Tru Color grout; it never needs to be sealed and has some flexibility even when fully cured out.
We still use vinyl pans. When done well they sit just fine and if you use the thicker one are very durable. We have switched to presloped wet bed the liner then finish slope. I have investigated schluter and it looks pretty interesting but seems inflexible and costly in some ways. I know for sure wetbed and vinyl works well and I see no reason to move away unless there is significant advantage. I can’t say I’ve ever heard of a problem with schluter shower but we do what has been working for years. We do add redguard as a topcoat to give extra protection especially in transitions. Lead pans I miss them.
I use a product called Schluter and have been using it for several years. A waterproof fabric that gets applied to the walls and the floor of a shower. I also give a warranty since using this.