Rather than equipping all of my models with altimeter or GPS telemetry, all one really requires, imho, is one model so equipped. Get a feel for where 400 feet is with such a model and then from there you can develop a mental point of reference.

Another thing to keep in mind, and mind you I am not and would not ever advocate intentionally breaking the rules, but... If you did an occasional flight that technically broke the 400 foot ceiling, say a loop that took you to 410 feet momentarily while you were diligently trying to be aware of staying withing the limits, no one is going to slap handcuffs on you because of it. For what I fly (helis and mainly park flyers) 400 feet is a good ways up and even before the new regulations I doubt I ever really flew above 400 feet. Just be reasonable and do your best to obey the limits and I think you will be fine.

Jim