The ones you're looking at look like pretty good deals to me as a lower budget hobbyist. They probably won't have the load regulation and protection characteristics of lab ones, but if they're modernized designs, they're probably very efficient and reliable compared to mine without being so extremely expensive as a lab supply. Shopping questions are prohibited, but I think it's fair to ask in a general sense how the power limitations of a PSU might work out for you assuming the supply lives up to them.
5A at 30V gives you about 150W to work with, 10A at 30V gives 300W. Less for properly simulating inductive loads, although for testing a motor the current limiting is usually useful up to its full rating, for testing a circuit that drives a motor you don't want to be either helping it out by limiting startup current or causing unrealistic brownouts in other parts of the circuit (Because most real sources droop rather than limiting current this way). RC land vehicles and large quadcopters or DC compressors are examples of high power motor load systems that might test the limits of the converters you're looking at. Motors are 80-90% efficent, so for just running a motor to test it assuming 80% efficiency, and that you found actual 5A and 10A 30V motors, you could test a 150W / 0.16 hp DC motor with the 5A supply or a 300 W / 0.32 hp DC motor
For LEDs 150W is a lot, probably the highest power single LED you'd want to play with would be 100W, which is silly bright, but your lesser supply would be capable of driving with a boost regulator. Then again a modular high power RGB driver could see surges of 3W per LED "pixel", so even an array of 100 for a sculpture might have peaks of 300W.
For processing loads, 150W is a lot.
Audio loads can be arbitrarily high.
For heater loads, you could plausibly want a very high wattage, for cooling loads even more so, but compressors have been mentioned.
If you use voltage converters, you'll lose 5 to 20% of that power in conversions (As little as 2%, but I'm not sure that can be done without an engineering degree), but you'll have the remaining power available at whatever voltage you want, within reason. Chances are you are really planning for one source voltage for most large projects and you need converters anyway. This is the model I usually use. I use the voltage supply to simulate a battery voltage and build whatever I need for the circuit off that. Last thing I breadboarded was an attempt at a driver for a 100W LED. I used 12V input with a 5V control circuit to drive the LED at 36V through a boost converter. I managed to drive the LED at about 20W because of limitations of the inductor I chose, and for the boost and cuk topologies I built, input current is continuous, so it won't set off your current limit until you get very close to it.
If you're trying to build a buck or buck/boost or any type that has discontinuous input current, the wattage you can make use of will be lower unless you filter the input to reduce current surges. If the filter is efficient enough, this will help you squeeze efficiency when you switch to a real battery. If it is not, you're better off without it in the end device, in which case you'd be better off with a supply that can simulate the current surges a battery can supply.
If you're wanting to design a boost driver your wattage is limited by the input voltage you want to simulate. A single Lithium-ion cell voltage of 3.6V gives you 18W to work with at 5A or 36W to work with at 10A. You could get around this by adding a voltage converter, but it's less convenient.