Where you have 100% Signal Quality on all channels and Signal Strength ranging from 60 - 85% then you really do not need a powered splitter... at all... no way. You've pretty much nailed the perfect score with that passive splitter.
Quality is by far the most important aspect of the Freeview signal. Strength isn't a big deal at all.
Any powered splitter can add strength, but all that is in reality is the equivalent of loudness of signal. The thing with digital TV is once the signal strength is above a minimum threshold then nothing improves. In fact, throw too much amplification at a signal and you'll actually do some real damage to the Quality, and this is over and above the extra noise that an amplified splitter contributes.
Quality, on the other hand, is a rare and fragile thing. There's only one place it comes from, and that's the aerial. Everything else in the signal chain either (at best) maintains it, or degrades it. Passive devices such as your splitter will do no harm to Quality. The cost is only a small loss in strength, and as long as there's sufficient strength to meet the minimum threshold plus a bit of a safety margin, then Strength really isn't that important. Amplified splitters add noise, and the result is a loss of Quality.
Stick with what you have. There's no reason to change. All it will do is cost you extra money and make the Quality worse.
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